Epidemiological Aspects

#### **Chapter 1**

## History of Dengue Fever Prevalence and Management in a One Health Perspective in Hainan Island, China

*Qingfeng Guan, Archana Upadhyay and Qian Han*

#### **Abstract**

Dengue fever (DF), a mosquito-borne viral infection common in warm, tropical climates, is an acute infectious disease caused by the Dengue virus (DENV). Geographically, Hainan Island falls in the southern belt of China holding an approximate area of 33,920 km2 . Meteorologically, Hainan is characterized to have a tropical maritime monsoon climate, giving rise to favorable natural conditions for different mosquito species. However, the diversity of mosquitoes and their abundance has undoubtedly put the island at a higher risk of mosquito-borne viral disease outbreaks. In this chapter, we have discussed the prevalence, control, and management of DF in Hainan Island in China along with the different species of mosquitoes responsible for transmitting the virus. In addition, future prospective of some important DF management strategies, related research methods, and integrated control strategies for the effective control and management of DF with One Health perspective has been summarized.

**Keywords:** dengue fever, dengue virus, Hainan Island, mosquito monitoring and control, one health

#### **1. Introduction**

Since the first reported outbreak in 1779 in Jakarta, Indonesia, many such outbreaks have taken place globally in tropical and sub-tropical climates majorly in urban and semi-urban areas having a wide array of weather conditions [1]. In this major outbreak, DENV type 3 was the causative agent, which was believed to be imported from countries in southeast Asia. Since then, several other imported DF cases have led to major and minor outbreaks in provinces like Guangxi, Yunnan, Hainan, Fujian, etc., in China [1]. Two major outbreaks of DENV type 1 and DENV type 3 were recorded, during 2006–2007 and 2012–2015, respectively [2]. From 1978 to 1991, DF outbreaks in China were mainly concentrated and limited to the coastal areas such as Guangdong and Hainan Province [2]. Hainan experienced the highest incidence rate between the years 1978 and 1992. However, fewer cases have been reported since then.

#### **2. History of DF prevalence in Hainan Island, China**

Hainan occurs as the southernmost province and the second largest island in China, having Guangdong province across the Qiongzhou Strait to the northern part of China (**Figure 1**). It boasts of a tropical monsoon climate experiencing rainy season during the months of May till October. The overall climatic conditions are suitable for the breeding of *Aedes* mosquito larvae and for the optimal transmission of DF. Hainan province has experienced three DF epidemics in the past. DENV type 3 was the causative agent for the first outbreak caused in 1978, followed by another outbreak in 1985–1988, and a third one, a dengue hemorrhagic fever in 1991, both of which were caused by DENV type 2 [3, 4]. In October 1979, a large number of suspected dengue cases were found in the northern coastal areas of Dan County (Danzhou city), Hainan Island. Later, the disease spread rapidly along the coastline *via* the transportation lines to the neighboring ports. By 1980, a total of 18 counties/cities and 208 towns, mainly falling in the coastal areas around the island, were facing a major outbreak [3]. In this period, 437,469 DF cases occurred in Hainan Island, and the infection rate was found to be 74% [3, 4]. Its long epidemic period and high incidence rate were of great significance in the epidemiological history. However, the incidence rates decreased significantly in 1981 and almost declined in September 1982 [3].

In early September 1985, suspected dengue cases were reported in Ganchong district along the northern coast of Dan County. Yangpu Township in the county became the local epidemic epicenter in mid-October and reached its peak in late October, which led to further spread of the infection. Neighboring townships in the Ganchong area started experiencing the incidence rates leading to a peak in early November. In late October, most of the adjoining areas along the northern coast started reporting patients, which caused several local outbreaks. However, in late November, cases invaded Changjiang, Lingao counties, and Haikou city, and still outbreaks occurred in a few areas of Changjiang. The outbreak hit Dan, Changjiang, Lingao counties, Haikou city, and 25 towns, with 12,449 cases reported in 3 months having an incidence rate of 210.68/100,000 and 28 deaths. The mortality rate of this

#### **Figure 1.**

*Geographical representation of the map of Hainan, China, highlighting the prominent cities and counties of the province. A: Map of China, localizing and highlighting Hainan Island. b: Map of Hainan Island displaying different counties and cities harboring different species of mosquitoes due to its typical tropical climate. Three mosquito species were labeled on the map. Map of China was downloaded from the web of Ministry of Natural Resources of the People's republic of China (http://bzdt.ch.mnr.gov.cn/browse.html?picId=%224o28b0625501ad13 015501ad2bfc0690%22). Map of Hainan Island was downloaded from the web of d-maps (https://d-maps.com/ carte.php?num\_car=21235&lang=en).*

*History of Dengue Fever Prevalence and Management in a One Health Perspective in Hainan… DOI: http://dx.doi.org/10.5772/intechopen.109737*

prevalence was 0.47/100,000, and case fatality rate was 2.25 per thousand [5]. In the first half of 1986, the epidemic had gone down owing to the early diagnosis and appropriate control measures of the epidemic. Subsequently, the prevention and control measures failed to persist for a long time, and it gave rise to new waves of epidemic, and finally led to an island-wide pandemic in August and September 1986. In 1986, 113,589 cases were reported, and 289 people died, affecting 182 townships and 27 farms in 18 cities and counties [6]. By 1987, the epidemic had gradually declined, with 30,229 cases and 76 deaths. In 1988, 7379 cases were reported and 18 deaths were reported. By the end of 1988, the outbreak had ended. The 1985–1988 epidemic was due to the DENV type 2 [7].

From June to November 1991, the third epidemic broke out in five cities and counties, with 13 villages and 3 towns falling prey to the epidemic. 521 cases were reported, most of which were mild. 92.3% of the patients were uninfected during the 1985–1988 epidemic, and only 6.8% were reported to have dengue-like symptoms [4, 8, 9].

In 2019, a total of 291 dengue cases were reported in Haikou, with an incidence rate of 12.64/100,000, including 251 local cases (86.3%) and 40 imported cases (13.7%). Among the imported cases, 32 imported cases were reported from Cambodia and Thailand, and 8 imported cases were reported, mainly from Guangxi and Yunnan provinces. All locally confirmed cases were found to be type I, while in the imported cases, all types were reported [10].

#### **3. DENV and its molecular and immunological characterization and identification**

Diagnosis of typical cases during epidemics is easy, but the diagnosis depends on virus isolation and serological examination. However, due to lack of awareness, it is easy to miss diagnosis in early epidemics, and other grades of fever may be misdiagnosed as DF. Therefore, DF should be distinguished from influenza, leptospirosis, measles, scarlet fever, and epidemic hemorrhagic fever. In Hainan, malaria needs to be excluded first [11].

DENV is an RNA virus that can be classified in Flavivirus genus of the Flaviviridae family. Being an RNA virus, its genome is undoubtedly prone to mutations, which makes it widespread. DENV has five antigenically different but very closely related serotypes (DENV-type 1, DENV type 2, DENV type 3, DENV type 4, and DENV type 5). The genetic sequences of the DENV1, DENV 2, DENV 3, and DENV 4 are well defined. However, they have some differences in their antigenicity, which makes them graded as reference strains. DENV 1 strain was isolated from Hawaii (DENV-I, Hawaii strain), with DENV 2 from New Guinea (DENV-II, The New Guinea strain), DENV 3 (DENV-III, Philippine H87 strains), and DENV 4 (DENV-IV, Philippines strain H241 strain) from the Philippines. Since then, a large number of DENV strains have been isolated from all over the world. Although some scholars have advocated the classification of some emerging strains with special molecular and immunological characteristics categorizing them into class V serotypes, but the theory has yet to be validated and widely accepted. DF is a mosquito-borne viral infection that gives rise to a sudden onset of fever followed by symptoms such as headache, nausea, muscle and joint pain, and rashes on the skin. It can affect any person but leads to serious complications in immunocompromised people, which can turn out to be fatal. This type of infection can become more fatal and can be named dengue hemorrhagic fever. It can be a life-threatening condition, which may further give rise to the critical form

of infection called dengue shock syndrome. Individuals who have been infected by one DENV serotype can usually have lifelong immunity to the same type of virus but have only partial or temporary protection against the other serotype viruses. Therefore, people living in dengue-endemic areas may develop infections with 4 DENV serotypes. Furthermore, there are common antigen-determination clusters between the 4 DENV serotypes and other members of the flavivirus family, with the presence of cross-reactive antibodies, and hence, the serological identification of different types of DENV becomes complex.

A wide range of laboratory diagnostic procedures have been developed and are in place for confirming DENV infection, which includes the classical method of isolation of the DENV, several molecular-based assays like PCR-based assays for testing the virus, serological assays like antigen or antibodies, or a combination of several assays. DENV can be isolated from the patient specimen or can be detected as the viral nucleic acid or as an antigen, IgM antibody in the blood. A blood specimen with a positive IgM or IgG antibody cannot confirm DENV infection, and can only be clinically diagnosed as suspected or possible cases as acute or convalescent serum samples.

#### **3.1 DENV infection and the body's immune response**

The incubation period of the virus ranges between 3 and 14 days, and it can be detected within 4 to 7 days of infection [12]. In many cases, even after collecting the biological specimens during the incubation period, it still at times fails to detect the virus or the corresponding body's immune response. After the onset, the presence of the virus in the blood (viremia period) is about 7 days, and the viral NS1 antigen exists in the blood for a slightly longer time. Within 4 to 5 days after the onset of the disease, the virus can be isolated from the patient's serum, plasma, white blood cells, cerebrospinal fluid, and autopsy tissue specimens, and the detection rate of viral nucleic acid and NS1 antigen is found to be higher during this period. Antibody levels in the patient's blood vary significantly depending on their individual immune status. If the patient has not been previously infected with DENV or other flaviviruses or has received flavivirus vaccine (e. g., Japanese encephalitis, yellow fever, etc.), the first infection slowly increases the levels of specific antibodies, and IgM antibodies appear the earliest, followed by IgA and IgG antibodies. The detection rate of IgM antibodies was about 50% in patients from 3 to 5 days after onset, about 80% in patients from day 5 after onset, and about 99% in patients from day 10 after onset. IgM antibody level reaches the peak 2 weeks after onset, then they gradually decrease followed by which they can be maintained for 2 to 3 months. The IgA antibody usually develops slightly later than the IgM antibody and persists for approximately 45 days [12]. One week after the onset, lower titer of IgG antibody can be detected in the blood specimen, after which the antibody titer persists for several months or even for lifetime. If a patient is reinfected with DENV (previously infected with, or sometimes possibly vaccinated against, or infected with other flavivirus vaccines), antibody titers can rise rapidly and react to a variety of flaviviruses. Mainly high levels of IgG antibodies can be detected in the acute phase of infection and persist for more than 10 months, even for lifetime. IgA antibodies can also be detected in the acute phase specimens. The IgM antibody titers in the early stages of the recovery period are significantly lower than the first infection, or can even be negligible. The application of IgA antibody detection system for detection of the antibodies is still in the evaluation stage.

*History of Dengue Fever Prevalence and Management in a One Health Perspective in Hainan… DOI: http://dx.doi.org/10.5772/intechopen.109737*

#### **3.2 Selection of appropriate detection methods**

In the early stage of the disease (within 5 days of onset), virus isolation, nucleic acid detection, or antigen detection methods are the most commonly used techniques and methods for diagnosis. When the course of the infection enters the recovery period (after 5 days of onset), serological detection using virus-specific antibodies is generally used for diagnosis.

Virus isolation: Classical isolation of the virus by cell culture methods is the most opted method for the isolation of the virus. It requires a biosafety level (BSL-2) laboratory and related necessary equipment. It is very important to maintain a cold chain during specimen transportation (frozen or refrigerated) for virus isolation. Specimens are usually inoculated in mosquito-derived cells (C6/36) or mammalian cells (BHK21, Vero) for isolation and culture. After the lesions are seen, the virus can be identified by detecting antigens or nucleic acid. Isolation of DENV can be taken as a confirmatory test, however, it takes long time and, therefore, it cannot be suitable for rapid diagnosis.

Nucleic acid testing: A variety of molecular biology-based reverse transcriptional polymerase chain reaction (RT-PCR) methods can be used for DENV nucleic acid detection, including one-step RT-PCR, real-time fluorescent RT-PCR, LAMP (Loop-mediated isothermal amplification assay), RT-RPA (Reverse transcriptase Recombinase Polymerase Activation). Nucleic acid testing identifies viral RNA within 1 ~ 2 days. The detection of viral nucleic acid in patient specimens can be confirmed and subtyped and can be used for early diagnosis. However, it has its own set of drawbacks as it is easy to produce false positives due to number of inhibiting factors, which requires strict zoning operation.

Antigen testing: NS1 antigen detection is commonly done using ELISA method or rapid detection reagent, which can be completed in several minutes to several hours. It is suitable for field and point-of-care settings. It forms an important approach toward acute DF diagnosis, which can be detected within 1 day after the onset, and few other reports have also stated that it can still be detected in blood specimens after 18 days of the onset. Due to the specificity of the NS1 antigen detection method, it can also be used in the differential diagnosis of flavivirus infection.

IgM antibody detection: Capture method ELISA (MAC-ELISA) for IgM antibody detection is the most commonly used detection method, and there are many commercial fast test reagents available for IgM antibody detection, which, however, cannot be used for serotype detection. At present, the detection reagents mainly detect viral envelope protein-specific antibodies, and the major drawback of these tests is that it shows a cross-reaction with other flaviviruses. A positive IgM antibody in the specimen, suggesting that the patient may be newly infected with DENV, is suitable for early diagnosis of DF. However, it is not suitable for single specimen. Even after reinfection, the IgM antibody titer base in blood specimens can still not be detected at times, affecting the diagnostic accuracy for detection of IgM antibodies.

IgG antibody detection: DENV IgG antibodies cross-react with other flaviviruses. IgG antibody test can be used to identify the first; if the acute phase specimen IgG antibody is negative and the recovery phase is positive, it can be determined as the first infection. If the convalescent blood sample is IgG antibody titer than in the acute phase (the two specimens should not be less than 7 days apart). Collecting the second specimen for diagnosis is of great significance for dengue prevention and control, especially in non-endemic areas.

Detection of neutralizing antibodies: The plaque reduction neutralization test (PRNT) and neutralization experiments can be used to detect neutralizing antibodies in the serum, which are the most specific serological tests and have a scope of further typing. However, it requires a contained laboratory infrastructure and is time consuming, therefore, it is not deemed to be suitable for early and quick diagnosis. In this method, the levels of convalescent serum-neutralizing antibodies can be confirmed using this test.

#### **4. Mosquito species and temporospatial distribution in Hainan Island**

Hainan province, which is located in the southernmost part of China and is dominated by a tropical Marine monsoon climate, with an annual average temperature of 24.2°C, an average annual rainfall of 1684 mm, and an average relative humidity of 85%. It has the most optimum natural conditions, which are very suitable for mosquito breeding and reproduction. At the same time, under the background of the establishment of the international tourism island and the promotion of the Belt and Road policy, the tourism, trade, and personnel exchanges in Hainan province increase, which gives rise and provides favorable conditions for the infectious diseases mediated by mosquitoes, and further give rise to hidden dangers of disease transmission. Mosquitoes can act as the transmission mode of various viruses and can lead to the epidemics and outbreaks of various mosquito-borne infectious diseases. The mosquitoes in Hainan Province include *Ae. albopictus* (**Figure 2c, f**, & **i**), *Ae. aegypti* (**Figure 2b, e**, & **h**), *Culex tritaeniorhynchus*, *Cx. pipiens pallens*, *Cx. quinquefasciatus* (**Figure 2a, d** & **g**), *Armigeres subalbatus*, *Anopheles dirus*, *An. sinensis*, *An. tessellates*, *An. minimus*, *An. arbumbrosus*, *An. barbirostris*, *An. vagus*, *An. anthropophagus* [14–30] (some distributions were shown in **Figure 1b**).

*Ae. albopictus* belonging to the genus *Aedes*, is a small and medium-sized black mosquito species and is the vector of DENV and chikungunya virus. *Ae. albopictus* is widely distributed in Hainan Province, mainly in Sanya city [13, 14], Danzhou city [15], Qiongzhong County [14], Lingshui County [14], Lingao County [15], and Baoting County [16, 17].

*Ae. aegypti* also belonging to the genus *Aedes*, is a dark brown or black medium mosquito species and is an important vector of arboviruses such as Zika virus, DENV, yellow fever virus, and chikungunya virus. It is the dominant mosquito species of DF found in Hainan Province. *Ae. aegypti* is widely distributed in Hainan Province, mainly in Sanya city, Danzhou city, Qiongzhong County, and Lingshui County [18–20].

Although the following mosquitoes do not transmit DENF, we have listed them as a reference for any implication of other vector-borne diseases control. *Cx. tritaeniorhynchus* (**Figure 1b**) belonging to a small brown mosquito species, is an important vector of Japanese encephalitis virus in Hainan Province. They are widely distributed in Haikou city, Sanya city, Dongfang city, Qiongzhong County, and Baoting County and are dominantly found in Haikou city and Dongfang city [21, 22]. *Cx. pipiens pallens* belonging to the genus *Culex*, a hazel small and mediumsized mosquito species is the vector of epidemic Japanese encephalitis virus. It is mainly distributed in northern China and found scantly distributed in Hainan Province [15]. *Cx. quinquefasciatus* belonging to the genus of *Culex*, a mediumsized mosquito species of red brown or light brown, is a vector of various diseases such as Japanese encephalitis in Hainan Province. It is found well distributed in

*History of Dengue Fever Prevalence and Management in a One Health Perspective in Hainan… DOI: http://dx.doi.org/10.5772/intechopen.109737*

#### **Figure 2.**

*Morphology of Culex quinquefasciatus, Aedes aegypti, and Aedes albopictus. a, d, and g: fourth instar larva, female adult and male adult of Cx. quinquefasciatus, respectively. b, e and h: fourth instar larva, female adult and male adult of Ae. aegypti, respectively. c, f, and i: fourth instar larva, female adult and male adult of Ae. albopictus, respectively. Photos of Cx. quinquefasciatus and Ae. albopictus were kindly provided by professor Jinbao Gu from the Department of Pathogen Biology, School of Public Health, southern medical university, Guangzhou, China. Photos of ae. Aegypti were provided by Dr. lei Zhang, Laboratory of Tropical Veterinary Medicine and Vector Biology, School of Life Sciences, Hainan University, Haikou, China.*

Haikou city, Sanya city, Dongfang city, Qiongzhong County, and Baoting County, and is most dominantly found in Sanya city and Qiongzhong County. However, in the last few years, it has also started appearing dominantly in Haikou city [19]. *Ar. subalbatus* belonging to the subfamily Culicinae, is a large brown-black mosquito species that is the vector of epidemic B encephalitis, which is primarily distributed in Haikou, Sanya, and Baoting County [22]. *An. dirus*, belonging to the genus *Anopheles*, is a gray-brown medium-sized mosquito species that have lesser transmissibility, but can spread other diseases and can endanger health. Hainan province is the main place where *Anopheles* mosquitoes thrive, and are distributed in the areas rich in mountains, jungles, and water systems, such as Wuzhishan city, Qiongzhong County, and Baoting County in the Wuzhishan area, and Dongfang city and Danzhou city along the coastal coast, and hence they are all active areas of *Anopheles* mosquitoes [23–25]. *An. sinensis* is widely distributed in Hainan Province and is widespread in majority of the regions of the province. The areas where these mosquitoes are densely distributed include Haikou city, Sanya city, Changjiang County, Qiongzhong County, and Lingshui County [26–29]. *An. tessellates* belonging to the genus *Anopheles*, are widely distributed in Hainan Province, mainly in Haikou city, Sanya city, Wuzhishan city, Lingshui County, and Lingao County [28]. On the other hand, *An. minimus*, belonging to the genus *Anopheles*, is a tan small

and medium-sized mosquito species. It mainly spreads nonviral diseases, causing serious harm. It is widely distributed in Hainan Province, mainly in Danzhou city, Qionghai city, and Tunchang County [30]. *An. arbumbrosus* belonging to the genus *Anopheles*, is found in Hainan Province, but has a small population, and is mainly found in Wenchang city, Qionghai city, Lingshui County, and Ding'an County [28]. In addition, *An. barbirostris* belonging to the genus *Anopheles*, is widely distributed in Hainan Province, mainly in Dongfang, Wenchang, Qionghai, Lingshui, and Chengmai counties [31]. However, *An. vagus* belongs to the genus *Anopheles* and is less distributed in Hainan Province [28]. *An. anthropophagus*, belonging to the genus *Anopheles*, is a gray-brown medium-sized mosquito species that have not been shown to transmit viral disease. In China, *An. anthropophagus* is distributed in Haikou and Wenchang, Hainan Province [32].

#### **5. Control and management of DF and mosquitoes with One Health perspectives**

There is no effective vaccine to date to prevent DF, and most human population is susceptible to the disease. After recovery from infection caused by one serotype, individuals have lifelong immunity to that particular serotype of the virus but lack completely against the other three serotypes. Thus, people living in DF endemic areas may develop infections with DENV type 4 as well in future.

Since 1987, Hainan had spent three years comprehensively controlling the *Ae. aegypti* mosquitos. In 1987, it was in the stage of full implementation planning. Where *Ae. aegypti* mosquitoes exist, measures were carefully implemented according to local environmental and social conditions, and it was required that the Breteau index be controlled below 5 by the end of the year. In 1988, preventive measures and regular management continued to be implemented. By the end of the year, all villages (neighborhood committees, farms) having *Ae. aegypti* mosquitoes had the Breteau index below 5. In 1989, it was the stage of consolidation and validation of the mosquito management. By the end of the year, the Breteau index of *Ae. aegypti* in villages (neighborhood committees, farm companies) was kept below 1. In addition, from 1987 to 1989, two representative villages from each city and county were selected to monitor DF and *Ae. aegypti* mosquitoes annually. The main technical measures in this plan were to adhere to the comprehensive control of mosquitoes in both larval and adult stages, and the specific measures were as follows.

Mosquito larval control: Basic measures include pouring out water in the water tanks, changing the water once every 3 ~ 5 days, adding a lid to some water tanks, and removal of small stagnant water indoors and outdoors. Biological mosquito control includes that water tank was stocked with mosquito fish, *Macropodus opercularis (Syn. M. chinensis)* or *Silurus asotus*, with 1 ~ 2 fish in each tank. Tanks were checked frequently after stocking. For fish that escaped or died, it was necessary to replace them in time. *Bacillus thuringiensis* was placed in water tanks or wells and towers every 7 days.

Adult mosquito Control: Pesticides, such as dichlorvos, fenitrothion, and others, were chosen for spraying so as to kill adult mosquitoes. Villages with a Breteau index of more than 20 (neighborhood committees, farm companies) were subjected to spraying with pesticides twice in February ~ April 1987, each time with an interval of two weeks. The spraying dose was 40 ~ 60 mg of 80% dichlorvos emulsion or

*History of Dengue Fever Prevalence and Management in a One Health Perspective in Hainan… DOI: http://dx.doi.org/10.5772/intechopen.109737*

50% chlorvos emulsion per cubic meter room. Doors and windows have to be closed when spraying. During the prevention and control period, once DF occurs, pesticides should be sprayed on the epidemic points or epidemic areas in time to kill poisonous mosquitoes.

In One Health perspective, the health and lifecycle of the zoonotic disease vectors should be explicitly considered alongside the human environment, demographics, and interaction with the zoonotic host vectors. In addition, continuous monitoring from epidemiological point of view has to be taken into consideration [33]. In addition to the increasing range of DENV infection and higher number of infected persons, the increasing frequency of international exchanges, elevation of the urban population, and the lack of effective control measures leading to the deterioration of urban environment and rise of mosquito growth, also needs to be further studied. And these factors along with geographical distribution of DENV make the presence of mosquito transmission vectors even wider.

#### **6. Integrated control and management strategies of DF with One Health perspectives**

Certain biological and synthetic control strategies can balance and manage the social, economic, ecological, and health benefits, which has to be carried out in a timely manner and help in combatting the disease in a better manner.

Additionally, carrying out timely and effective vector biological monitoring, practical risk assessment, control, planning, and preparation of vector biological and related diseases, orderly selection of environmentally friendly control technology and comprehensive measures would directly help in eradication. The following six main components of mosquito prevention and control in Hainan Island are as follows:


### **Acknowledgements**

This study was supported by the Major Science and Technology Plan of Hainan Province (ZDKJ2021035), the National Natural Science Foundation of China (U22A20363), and Hainan Provincial Natural Science Foundation of China (821RC530).

### **Conflict of interest**

The authors declare no conflict of interest.

### **Author details**

Qingfeng Guan1,2, Archana Upadhyay1,2 and Qian Han1,2\*

1 Laboratory of Tropical Veterinary Medicine and Vector Biology, School of Life Sciences, Hainan University, Haikou, Hainan, China

2 One Health Institute, Hainan University, Haikou, Hainan, China

\*Address all correspondence to: qianhan@hainanu.edu.cn

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*History of Dengue Fever Prevalence and Management in a One Health Perspective in Hainan… DOI: http://dx.doi.org/10.5772/intechopen.109737*

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**Chapter 2**

## Dengue Fever in Pediatrics

*Neydi Osnaya Romero, Sandra M. Villagomez Martinez, Ivan Pilar Martinez and Virginia Diaz Jimenez*

#### **Abstract**

Dengue continues to be a health problem in the world, according to data from the PAHO. In recent years, dengue cases have been reported from 505,430 cases in the year 2000 to 5.2 million in the year 2019; among the most affected groups are those under 15 years of age. Dengue is a viral disease caused by a virus of the Flaviviridae family, of the Flavivirus genus. It is a disease that requires the bite of the female Aedes aegypti mosquito; the incubation period varies from 8 to 12 days. The pathophysiology of dengue is due to the alterations suffered by the endothelium when caused by the viral particle. Three phases have been identified: 1. the febrile phase; 2. the critical phase, in which patients develop systemic symptoms with a greater inflammatory response, with a risk of bleeding; and 3. the recovery phase. The main symptoms are fever, headache, retro-ocular pain, arthralgia, myalgia, and within the laboratory alterations are elevated hematocrit (hemoconcentration), leukopenia, and thrombocytopenia, among the complications, are pleural and pericardial effusion and ascites, as well like crash and death.

**Keywords:** dengue, dengue fever, dengue hemorrhagic fever, treatment, children

#### **1. Introduction**

Dengue continues to be a severe health problem in the world. According to data from the PAHO, despite the measures to try to contain the number of dengue cases, it continues to be a problem of public health in at least 100 countries. In recent years, dengue cases have increased, probably associated with the increase in urbanization of some areas. This situation conditioned an increase in cases from 505,430 cases in the year 2000 to 5.2 million in the year 2019, and of these 28,000 cases were serious, with a report of 1534 deaths. During the year 2020, of the reported cases of dengue fever, 66% of the deaths correspond to the group of patients under 15 years of age. By the year 2021, 1,324,108 cases of arbovirus were reported, and of these, 89% (1,173,674) of the cases corresponded to dengue fever, the highest incidence of cases is concentrated in the regions of Africa, America, the Eastern Mediterranean, Southeast Asia, and the Western Pacific. During the pandemic, although there was a decrease in infectious diseases, there was also an apparent decrease in dengue cases between 2020 and 2021. This decrease was attributed to an underreporting of cases during the COVID-19 pandemic. However, this decrease in the incidence of infectious diseases did not occur in all countries, since in some countries, such as Pakistan and Thailand, they observed an increase in infectious diseases that were already controlled, such as typhoid fever, measles, and dengue fever, after the confinement [1–4].

Dengue is a viral disease produced by a virus of the Flaviviridae family, of the Flavivirus genus, and there are four serotypes, DENV1, DENV2, DENV3, and DENV4. It is a disease that requires a vector for its transmission. The transmission of dengue fever is carried out by the bite of the female Aedes aegypti mosquito. The incubation period varies from 8 to 12 days, the onset of symptoms is related to the initial viral concentration, cases of dengue hemorrhagic fever have been reported more frequently in patients under 15 years of age, so review this topic as part of the diseases of the pediatric age. In some parts of the world, such as Asian countries, dengue fever has been considered a pediatric health problem. In Latin America, it was considered an entity with a higher incidence in the adult population; however, in recent decades, there has been an increase in the cases in the pediatric population, although not only the cases in the pediatric age have increased, but also the presentation of complications in this age group. Another problem that has been observed in some dengueendemic cities has been co-infections, con-infections with typhus have been found in India, and during the COVID-19 pandemic, cases of dengue with co-infections with the SARS-COV2 virus were documented in dengue-endemic countries, so in these places, particular interest should be paid to the symptoms of these patients in whom dengue fever is suspected [5–8].

Although it is true that this problem occurs in tropical places and with certain geographical characteristics, we must not forget that it can also be a traveler's disease and that symptoms develop once the patient has returned to their place of origin, so that if a patient presents a fever that is difficult to control, accompanied by headache, joint pain, rash and/or signs of bleeding after traveling to a tropical area, the diagnostic possibility of dengue fever or dengue hemorrhagic fever should be investigated, as the case may be. The cases have been increasing in countries like Brazil, which entails, in addition to being a health problem, an increase in the economic requirements to handle this increase in cases [9, 10].

The diagnosis of dengue fever is established by identifying those tested for the virus from the sixth day by the Enzyme-Linked ImmunoSorbent Assay ELISA technique or by PCR). These tests will be carried out after the fifth or sixth day. Return day for greater diagnostic certainty [9].

#### **2. Clinical manifestations**

The pathophysiology of dengue is derived from the alterations suffered by the endothelium when infected by viral particles and the inflammatory response secondary to the infection. During the inflammatory response, the non-structural protein 1 (NS1) of the virus adheres to the vascular endothelium, altering the vascular permeability of molecules and liquids, the coagulation pathways will also suffer alterations, vascular fibrinolysis events will be triggered, and secondarily alteration of platelet adhesion, which generates a problem of thrombosis. These alterations would explain the presence of complications in dengue hemorrhagic fever, the vascular damage will initially cause alterations in the permeability of the endothelium, which, if they persist, can cause lysis of the endothelial cells, once irreversible damage to the endothelium is established. This allows proteins and fluids to leak into the third space, this leak of extravascular fluid will result in hemoconcentration and elevated hematocrit, loss of intravascular fluid that translates as arterial hypotension, which if perpetuated can condition the shock phase, and the presence of complications that lead the patient to death [11–14].

#### *Dengue Fever in Pediatrics DOI: http://dx.doi.org/10.5772/intechopen.109719*

As part of the study of the inflammatory response, some studies have been carried out in which various cytokines have been identified. The type of cytokines that have been identified seem to be related to the infecting serotype in such a way that it has been found that in infections by In DENV2 serotype, the cytokines IL12p70, IL6, and TNF-α are found to be higher than in DENV1 infections; however, interleukin 8 levels are similar in infections by both serotypes. In patients with dengue fever, a greater number of Interferon IF-Ύ than in patients with dengue hemorrhagic fever, the fact that the DENV2 serotype is associated with a higher concentration of cytokines also makes it associated with infections with a greater inflammatory response, and therefore with a greater number of hospitalizations [12].

In a study carried out in Mexico, higher concentrations of IL-12p70, TNF-α, and IL-6 were reported in patients with hemorrhagic dengue fever with the DENV2 serotype than in patients with the DENV1 serotype. However, the levels of TNF-α, IL -12p70, and IL-6 were higher in patients with dengue fever than in patients with dengue hemorrhagic fever infected with the DENV1 serotive. Higher concentrations of interferon (IFN)-γ and IL-12p70 were observed in patients with dengue hemorrhagic fever. If we remember that these cytokines are proinflammatory, it is understood why they are found in higher concentrations in patients with dengue hemorrhagic fever, and why the increase in endothelial permeability results in hemodynamic and coagulation alterations in these patients. Cytokines related to the endothelial inflammatory process, such as IL-12p70, IFN-γ, TNF-α, and IL-6, were higher in patients with dengue hemorrhagic fever. If we remember that these cytokines are pro-inflammatory, it is understood why it is found in older patients. Concentration in patients with dengue hemorrhagic fever and the reason for the increase in endothelial permeability, which allows capillary leakage of fluids, would explain the hemoconcentration, decreased intravascular flow, hypotension, and a greater risk of presenting a state of shock and complications, such as pleural and pericardial effusion and/or ascites [11, 12, 14].

It is evident that the inflammatory response of the patient will depend on the infecting serotype. It must not be forgotten that the different serotypes may be circulating in the same region, it will also influence the response if it is a primary infection or reinfection, either by the same serotype or a different serotype will also affect this response if the patient has other comorbidities, such as arterial hypertension, some immune deficiency or any history that affects the patient's immune response [12, 14].

The clinical symptoms of dengue in pediatrics are variable and sometimes milder than in adults. However, three stages have been described: the febrile stage, the critical stage, and the recovery phase.

In the febrile phase, it occurs between the second and seventh day, there is a fever of up to 40°C, which is mediated by the response of IL1, IL6, and TNF and in this phase, the viremia is recorded by the viral particle that circulates or is associated with lymphocytes, macrophages or platelets. This febrile phase can be accompanied by headache, which is holocranial with retro-ocular pain, myalgia, and arthralgia, predominantly in the long bones, lower back, and lower limbs. A rash that appears between the 3rd and 4th day; some patients show improvement during this phase; patients with a history of a previous infection may present a shorter febrile period and improve or advance to the severe phase [8, 12, 15].

It is in the critical phase that the inflammatory response will cause alterations in the endothelium, which together with hypoalbuminemia will condition the leakage of capillary fluid, favoring the presence of pleural effusion, ascites, and edema in the extremities. At this stage, bleeding data, such as epistaxis, hemorrhages in the skin (petechiae) and mucous membranes, digestive tract can be presented; liver failure

may also occur. It is in this phase that hypovolemic shock, due to hemoconcentration, can occur neurological problems, such as encephalitis, that can be caused by liver failure, should not be ruled out. Dengue shock must be managed in an intensive care area since that if not handled properly can cause the death of the patient. During the follow-up of a patient with a diagnosis of dengue fever, one should be aware of some symptoms that have been described as alarm data that could precede the state of shock, such as abdominal pain, vomiting, drowsiness, and hepatomegaly [13, 14].

During the recovery phase, it is accompanied by the normalization of laboratory abnormalities, such as thrombocytopenia and correction of coagulation times with the consequent reduction in bleeding risks. The recovery phase can appear from 2 to 3 days after the end of the critical phase, also during this phase an itchy maculopapular rash can be observed, it must be taken into account to make the differential diagnosis with Chinkungunya [10, 16–18].

Laboratory studies should be requested in those patients who observe risk factors, such as blood count, coagulation tests, transaminases, and ammonium levels. In case the patient presents disorders of the state of consciousness, with these studies, we can document hemoconcentration when finding elevated hematocrit, which would be an indication for the use of intravenous crystalloids, decreased platelet count (thrombocytopenia), if the patient has active bleeding or is at risk of bleeding, transfusions of platelet concentrates should be performed. With the determination of the coagulation times, if an alteration occurs, the administration of fresh frozen plasma or vitamin K can be indicated as required. In patients with altered state of consciousness and elevated liver transaminases, serum ammonium concentration should be determined, if elevated, antimony measures should be installed. Imaging studies such as a chest X-ray can help us document the presence of a pleural or pericardial effusion; an


#### **Table 1.**

*Signs and symptoms observed in patients with dengue from 2018 to 2022 at the hospital den Niño Morelense (HNM) Mexico.*


**Table 2.**

*Laboratory changes reported in HNM patients with dengue in the period 2018–2022.*

abdominal x-ray or an abdominal ultrasound would help us determine the presence of ascites [12–14].

In a pediatric hospital, in the state of Morelos HNM (Hospital del Niño Morelense) in Mexico, a study was carried out from 2018 to 2022 of patients diagnosed with dengue, 105 patients were obtained, finding the following results, the average age was 9 years with DS + -4.1 years; 61% of the patients only presented dengue fever in the febrile phase, while 38% presented symptoms that placed them in the critical phase, and only 1% presented shock data; 100% of the patients presented fever; headache 53.3%; asthenia and adynamia in 45.71% and alarm data, such as abdominal pain, in 38.09%; 33.3% vomited and 10.47% reported hepatomegaly, 29.52% reported bleeding in the mucous membranes, 8.57% petechiae, and 1.9% hypotension (**Table 1**).

The first changes in the laboratory that can be detected in the febrile phase are leukopenia, thrombocytopenia, and increased transaminases. In the critical phase we find increased hematocrit, hypoalbuminemia, prolongation of coagulation times. In the HNM study, laboratory determinations were also performed on the patients, and thrombocytopenia was found in 59%, hemoconcentration in 31.42%, leukopenia in 48.7%, increased transaminases in 72.13%, and hypoalbuminemia in 33.3% **Table 2** [13].

Regarding complications in this series of HNM patients, pleural effusion was found in 5.71%, hemorrhage data in 4.76%, ascites in 1.9%, pneumonia in 0.95%, acute liver failure in 0.95%, and hypovolemic shock in 0.95%. No case of encephalitis was documented and 4.28% presented more than a complication.

#### **3. Treatment**

Treatment so far is symptomatic, and there is currently a dengue vaccine indicated for people with at least one primary infection, thereby reducing the risk of severe dengue.

According to the indications of PAHO, it is suggested to classify patients for treatment, as patients with ambulatory management, hospitalized patients for observation, and hospitalized patients for intensive management.

In the first group, patients present with fever, arthralgia, and myalgia live in an endemic area for dengue fever, which is why the diagnosis of dengue is suspected. If there is no evidence of dehydration or shock, fluids and fluids should be indicated. Antipyretics, if possible, should be reassessed every 48 hours; monitoring of alarm data, such as abdominal pain, vomiting, drowsiness, and bleeding data should be

indicated. At this stage, paracetamol 10–15 mg/Kg/dose can be used with a maximum dose of 4 g in 24 hours, in children, remember not to use salicylates, once the patient has been identified, it is advisable 48 hours after the onset of the symptoms to take a blood count to determine the hematocrit and platelet count [4].

Patients with any comorbidity, such as arterial hypertension, diabetes mellitus, asthma, hematological diseases, cardiovascular diseases, or some autoimmune disease, children under 5 years of age, pregnant patients, and patients at social risk (who have difficult access to hospitals) should be hospitalized for surveillance. For health services, it is important to maintain hydration, intravenous (IV) crystalloid solutions should be used in case of having a high hematocrit or if diuresis is <0.5 ml/kg/hr., insist on fluid intake and keep comorbidities under control. In these patients, hematocrit, platelet count, coagulation times (PT, PTT), DHL, and transaminases (ALT, AST) should be determined. In this phase, it is indicated to take serology to try to identify the serotype [10, 19, 20].

Patients who require shock management should start infusion of crystalloid solutions in a 20mlKg bolus to try to restore a mean arterial pressure according to their age, and management of colloid solutions should be evaluated according to the hemodynamic evolution. If a decrease in hematocrit is reported, hemorrhage should be suspected, so a transfusion of concentrated erythrocytes should be evaluated. If despite fluid management, the patient still has signs of hypotension, the use of inotropes should be evaluated. These patients, in addition to the laboratory tests that have been mentioned, tests should be taken to evaluate renal function, echocardiogram, chest, and abdominal X-rays in search of pleural effusion or presence of ascites and in case of neurological data, such as loss of state of consciousness or seizures, consider performing a head tomography, magnetic resonance imaging, and/or lumbar puncture; to evaluate his discharge he must be without fever, without data of hemodynamic alteration, normal platelet count, and normal hematocrit, as well as good tolerance to the oral route to be able to discharge him without risk of relapse [4, 9, 15].

It is a fact that after the COVID-19 pandemic, many things will change. In this case, we must not forget that both COVID-19 and dengue fever are viral diseases, or that they may share clinical characteristics, in addition to the fact that they must be to consider diagnostic possibilities when faced with a patient with fever or even not to forget that both infections can be present together. The diagnosis of dengue should be thought of as one of the traveler's diseases, so it is important to ask the patient about trips to dengue endemic places, and in this way, we can have cases of dengue fever in places where it is not endemic. The geographical and climatic conditions are not going to favor its spread, especially in communities where dengue fever is not endemic, however, it must not be forgotten that with changes in global climate conditions, the conditions for its spread can occur. Of dengue, as well as the appearance of different serotypes in regions where it is not common to find them [20].

#### **4. Prevention**

Prevention measures include the use of mosquito nets, avoiding the accumulation of scrap, and avoiding collections of stagnant water. Some authors have correlated the increase in urbanization with the increase in dengue cases, as well as the deficiency in the disposal of garbage from the communities; the use of repellents has modified the prevalence of the different serotypes, some studies reveal that people who have suffered from dengue fever will have better practices of preventive activities to avoid

*Dengue Fever in Pediatrics DOI: http://dx.doi.org/10.5772/intechopen.109719*

contracting the disease again. After the pandemic, it was observed that in some places, they improved their hygiene habits in order to reduce the risk of contracting COVID, and that improved the health of people in dengue-endemic areas, it is suggested that in endemic areas the health authorities should send information to the inhabitants in order to improve health education in these areas [21].

It should not be forgotten that dengue fever is also related to seasonal weather variability, and it is a fact that global warming is causing changes in many regions of the world, so the spread of arbovirus infections may be modified [18].

#### **5. Conclusions**

Dengue is a health problem and children are among the vulnerable groups. The clinical picture may be mild, presenting only fever and general state attack, but it should not be ruled out that each patient diagnosed with dengue fever may present hemorrhagic dengue, shock and death. So, it is important to know the clinical picture, diagnostic methods, management and, above all, in endemic areas, continue with the prevention and eradication programs of the A. aegypti vector.

#### **Conflict of interest**

The authors declare they have no conflict of interest.

#### **Financing**

This work has no funding.

#### **Abbreviations**


#### **Author details**

Neydi Osnaya Romero1 \*, Sandra M. Villagomez Martinez1 , Ivan Pilar Martinez<sup>2</sup> and Virginia Diaz Jimenez3

1 National Institute of Pediatrics, Mexico City, Mexico

2 Children's Hospital in Morelense, Morelense, Mexico

3 Pediatric Infectology, National Institute of Pediatrics, Mexico City, Mexico

\*Address all correspondence to: nenyos@prodigy.net.mx

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 3**

## Reemergence of Sylvatic Dengue Virus in Southern Senegal, 2021

*Idrissa Dieng, Cheikh Talla, Joseph Fauver, Mignane Ndiaye, Samba Niang Sagne, Mamadou Aliou Barry, Ousmane Faye, Amadou Alpha Sall and Oumar Faye*

#### **Abstract**

As part of the syndromic surveillance of fever in Senegal, the virology department at Institut Pasteur de Dakar (IPD) in collaboration with the Epidemiology Unit and the Senegalese Ministry of Health conducted syndromic surveillance of fever in Senegal. Sample are from all suspected arboviral infections patients attending any of the sentinel sites. Collected blood samples were sent on a weekly basis at WHOCC for arboviruses and hemorrhagic fever viruses for screening of seven medically important arboviruses, including dengue virus (DENV). From January to December 2021, 2010 suspected cases were received among them 124 for confirmed to be DENV+ by RT-qPCR attempt of serotyping led to the detection of atypical DENV case from Sare Yoba area (Kolda region) which is unable to be correctly assigned to a serotype by the available tools (TIB Molbiol Modular Dx Dengue typing kit). Performed genome sequencing et phylogenetic analysis leads to the identification of a sylvatic DENV-2 strain closely related to a virus previously detected in Guinee-Bissau in 2009. This finding constitutes proof of the contemporary circulation of DENV-2 strain belonging to the sylvatic cycle in addition to well-known epidemic strains; this adds a piece of complexity to dengue management in Senegal. Alarmingly, it calls for improved genomic surveillance of DENV to know the genetic diversity of circulating strains in order to strengthen future vaccination policies.

**Keywords:** fever, syndromic surveillance, Sénégal, sylvatic DENV, réémergence

#### **1. Introduction**

In Africa, fever is the primary symptom that prompts patients to seek medical attention [1, 2]. The presence of a fever of unknown origin has historically been used as a starting point for treating malaria [3]. As malaria control efforts in Sub-Saharan African nations continue to yield positive results thanks to measure as large-scale implementation of malaria rapid diagnostic tests (mRDT), the incidence of this disease is decreasing, resulting in a smaller percentage of febrile illnesses attributed to malaria. During the period from 2000 to 2013, malaria mortality rates decreased by 47% worldwide and by 54% in Sub-Saharan Africa, which is the region most affected by the disease. This decline has resulted in an increase in the proportion of patients

exhibiting symptoms of non-malaria febrile illness (NMFI) [4]. Among myriad of pathogens such as viruses, bacteria, and parasites can cause acute febrile episodes indistinguishable from malaria.

Dengue fever (DF) is a viral illness caused by the dengue virus (DENV) etiological agent of the disease. The virus exists in four serotypes, namely DENV1–4 [5]. They belong to *flaviviridae* family and *flavivirus* genus. DENV is prevalent in numerous tropical and subtropical regions worldwide [6]. The virus is considered a significant public health threat in these regions due to its high morbidity and mortality rates [7]. Infections with DENV cause clinical manifestations ranging from self-limited flu-like symptoms, namely dengue fever (DF) to life-threatening infection associated with hemorrhage and or shock syndrome called severe dengue [8]. According to World Health Organization (WHO) estimates each year 390 million people are infected by the virus [9] with a case fatality rate ranging between 1 and 5% [10, 11]. In contrast to American and Asian countries, the virus epidemiology is not well known in Africa despite reports of the virus circulation since the nineteenth century [12, 13]. This underestimation in the African continent is linked to many factors as low awareness, lack of surveillance activities, the prevalence of pathogens associated with similar clinical manifestations, and the lack of reliable diagnostic tools [13].

In Senegal since 2011, in collaboration with the Senegalese Ministry of Health, the virology department and the epidemiological unit of Institut Pasteur de Dakar (IPD) set up a countrywide surveillance of influenza viruses and other respiratory tract infections associated viruses, namely 4S network [14]. This system was improved in 2015 to add the surveillance of other pathogens. Thanks to noticed increased number of febrile cases around the country not linked to malaria; the list of targeted pathogens includes arboviruses (Dengue, Zika, and Rift valley fever), bacteria, etc. [15]. Following years, this human sentinel surveillance throughout fever permitted the isolation and identification of many viruses, including DENV. In 2017, Dieng and colleagues [16] implemented genomic surveillance of DENV in Senegal throughout the 4S network collected samples. This allowed the detection and mapping of molecular characterization of DENv serotypes/genotypes circulating around the country [16]. DENV serotypes are maintained in two different ecologically and evolutionary distinct transmission cycles, namely the human cycle and the sylvatic cycle. The human cycle is sustained exclusively between humans and domestic or peridomestic mosquitoes, while the sylvatic cycle involves arboreal mosquitoes and nonhuman primates [17]. Although sylvatic strains of DENV play a pivotal role in the evolution and emergence of the virus, there have been no documented cases of ongoing and uninterrupted transmission [18].

In Senegal, particularly in the southern region of the country (i.e., the Kédougou area), the predominance of sylvatic cycles has historically played a significant role in the spread of DENV [19]. Since 2009, there have been numerous reports of dengue epidemics in Senegal, all of which have been associated with the epidemic cycle. This chapter discusses the reemergence of contemporary sylvatic DENV-2 strain in Southern Senegal, thanks to implemented genomic surveillance and 4S network system.

#### **2. Material and methods**

#### **2.1 4S network sentinels sites for fever surveillance**

In Senegal, a Sub-Saharan African country, a surveillance system for febrile illnesses has been in place for a long time. The Senegalese Ministry of Health, the *Reemergence of Sylvatic Dengue Virus in Southern Senegal, 2021 DOI: http://dx.doi.org/10.5772/intechopen.110900*

WHO country office, and the Institut Pasteur de Dakar (IPD), which hosts the WHO Collaborating Center for Arboviruses and the National Influenza Center, partnered to establish a febrile illnesses surveillance network [20]. The system initially monitored virological surveillance of Influenza-like illnesses (ILI) but was later revised with the establishment of the Senegalese Syndromic Sentinel Surveillance Network (4S network) based on a syndromic approach centered around fever. The 4S network is accountable for monitoring febrile illnesses at 20 sentinel sites across 14 administrative regions in Senegal, where population-based surveillance for ILI and other priority public health syndromes, such as malaria, dengue-like syndromes, and diarrheal syndromes, are conducted. Outpatient visits are enrolled and distributed across various regions of the country [21].

#### **2.2 Sample collection**

Clinical samples were collected from 22 sentinel sites around the country. For each suspected/ case that meets inclusion criteria, whole blood samples were collected using dry tubes and stored at +4 until shipping to the reference lab located at the virology department at IPD.

#### **2.3 Sample shipping to reference lab**

On a weekly basis collected suspected arboviral samples are shipped with epidemiological and demographic forms at the virology lab based at Institut Pasteur de Dakar. At the lab, samples were identified and a unique number of six digits is provided.

#### **2.4 Sample handling and RNA extraction**

Briefly, dry tubes were centrifuged at 2000 rpm for 5 minutes and the serum was harvested on cryotubes and then stored at – 80 for biobanking purposes. For the purpose of molecular screening, RNA extraction was performed from 140 μl of serum using Qiagen viral RNA mini kit (Qiagen, Hildan, Germany), according to the manufacture's recommendations. RNA is eluted on 60 μl of molecular grade water and stored on ice until further use.

#### **2.5 RT-PCR diagnostic assays**

#### *2.5.1 panDENV detection*

RNA was detected using Lightmix 1 step (Roche). Master mix for virus detection was prepared according to the table (**Table 1**) using a set of primers targeting DENV 3'-UTR region previously described by Wagner and colleagues [22]. The real-time PCR assay was performed using a CFX96 thermocycler (Biorad, France). The thermal profile used is described in **Table 1**. Any DENV RNA with Ct values below 32 was considered positive.

#### *2.5.2 DENV serotyping assay*

In the case of panDENV positivity, same RNA was systematically subjected to RT-qPCR to determine the associated DENV serotype using TIB Molbiol Modular Dx Dengue typing kit (cat. no. 40–0700-24; TIB Molbiol, Berlin, Germany) [19]. Using


#### **Table 1.**

*Mixture preparation and conditions for RT-qPCR detection of DENV.*


**Table 2.**

*Mixture preparation and conditions for RT-qPCR DENV serotyping.*

different probes serotype-specific and labeled with different fluorophores, the system allows discrimination of serotypes from 5 μl of RNA input. Surprisingly, at the end of the reaction used system fail to define the serotype of DENV+ samples collected from Sare Yoba in the Kolda region in 2021 (**Table 2**).

#### **2.6 Sequencing of NS5 gene using nanopore sequencing**

Using a set of primers FU1/FD3 specific to the flavivirus genus and previously described by Kuno and colleagues [23] we amplify ≈ 1 kb of NS5 gene. Obtained amplicons were visualized on agarose gel and then purified at 1:0.8 ratio using.

AMPure beads (Beckman Coulter Inc., Brea, CA, USA). Purified DNA was subjected to library preparation and sequencing using Oxford Nanopore MinION (Oxford Nanopore Technologies plc, Oxford, UK). The Rapid barcoding kit (SQK RBQ110.96), which uses a transposase-based barcode binding was used during library prep steps. The prepared library was loaded onto the R9 flow cell and a sequencing reaction was performed MinION MK1C device. After 24 hours of run, the raw data were collected on flash drive; base called was performed using guppy (https://community.nanoporetech.com) to generate fastq files. Bioinformatic analysis was performed using in-house script; Nanofilt (10) was used to trim barcode adapters (options -headcrop 50 and -tailcrop 50). Minimap 2 was used to map reads to DENV-2 reference genome (NC\_001474.2) (11). Finally, generated consensus was subjected to National Center for Biotechnology Information (NCBI) BLASTn, which shows 99.66% identity with sylvatic DENV-2 (JF260983).

#### **2.7 Development of specific sylvatic DENV-2 primer scheme**

Since NS5 gene sequence provides a partial overview of virus genetic makeup based on the result from BLAStn using this gene. We downloaded full genome

sequences of closely related sylvatic DENV-2 sequences. Obtained dataset (n = 16) was aligned using MAFFT [24] and manually curated using geneious prime (Biomatters, New Zealand). Tilling PCR primal scheme was designed using the webbased tool (https://primalscheme.com/), and parameters sets to generate amplicons of around 900 bp and covering the coding region of sylvatic DENV-2 strains. Designed primers were synthesized generated by TIBMolBiol (Berlin, Germany), according to the manufacturer's recommendations.

#### **2.8 Sequencing of full coding DENV polyprotein using nanopore technology**

Amplicons were generated using Q5® High-Fidelity 2X Master Mix (New England Biolabs, Ipswich, MA, USA), according to a protocol previously described by Dieng and colleagues [25]. Briefly, primers were organized in two separate pools and then were used to generate overlapping fragments covering the full coding region of the detected sylvatic DENV-2 strain. Raw data were collected after 24 hours of sequencing and data analysis procedures were identical to those previously employed for NS5 gene sequencing.

#### **2.9 Phylogenetic reconstruction**

In order to establish and contextualize the evolutionary history of detected DENV strain, from Genbank database we downloaded representative sequences of described genotypes of DENV-2 and then aligned the resulting dataset using MAFFT [24]. We constructed a maximum likelihood (ML) tree using IQ-TREE [26] and then plotted the resulting phylogenetic tree and its associated metadata as years of sampling and host using R statistical software (version 3.6.0.).

#### **2.10 Data management and statistical analysis**

Patient information and results were recorded in a database, including patient ID, date of sample collection, and laboratory results. Weekly, the database was sent to Senegalese Ministry of Health for case notification and epidemiological report. Graphs were performed using the R statistical software (version 3.6.0.).

#### **3. Results**

From January 2021 to December 2021, 2010 blood samples suspected of arboviral infections were received at the WHOOC for arboviruses and hemorrhagic fever viruses. Samples were tested for DENV by RT-qPCR; among them, 123 shows dengue positivity. The algorithm for laboratory testing for DENV is presented in **Figure 1**.

The highest number of RT-qPCR DENV+ samples were recorded during the months of October and November with 53 and 63 confirmed cases, respectively (**Table 3**). At the serotype level, how most of the detected DENV-positive samples are DENV-3, followed by DENV-1, and finally DENV-2.

Untypable strain from Sare Yoba (Kolda region) was successfully sequenced using the proposed workflow (**Figure 2**).

Indeed, designed primers allow us to retrieve the nearly complete genome of the previously untypable DENV strain. Blast analysis shows that the strain is closely related to the sequences with accession number JF260983. The strain obtained during

#### **Figure 1.** *Diagnostic algorithm for DENV molecular testing and serotyping.*


#### **Table 3.**

*Samples tested for DENV and lab results from january, 2021 to December, 2021.*

*Reemergence of Sylvatic Dengue Virus in Southern Senegal, 2021 DOI: http://dx.doi.org/10.5772/intechopen.110900*

**Figure 2.** *Used workflow to identify and sequence sylvatic DENV-2 strain in Saré Yoba area (Kolda, region).*

#### **Figure 3.**

*Drawn maximum likelihood (ML) phylogenetic tree based on the nearly complete genome of DENV-2 sylvatic strain obtained during this study. The heatmap shows sequences genotype. The sequences obtained during this study are colored in red. The sylvatic genotype sequences are highlighted in light pink.*

this work shares 99.66% identity nucleotide identity with the sequence JF260983. Genotyping of the sequences using the dengue typing tool shows the isolate cluster on the sylvatic DENV-2 group. This was confirmed by performing a phylogenetic analysis (**Figure 3**).

#### **4. Discussion**

This chapter presents findings from molecular surveillance of DENV conducted in Senegal in 2021 using the 4S network system, which allowed for the detection of the first cases of DENV during multiple outbreaks [14, 19]. From January to December 2021, 123 confirmed dengue cases were obtained out of the 2010 collected samples (**Figure 4** and **Table 3**).

The molecular surveillance of identified strains provided insights into the distribution of DENV serotypes/genotypes in Senegal [16]. We encountered a patient with an unusual dengue case in November 2021, and despite obtaining a high Ct value of 26.04 using the panDENV assay, we were unable to determine the virus serotype. Using the designed workflow (as shown in the figure), we were able to detect the presence of contemporary sylvatic DENV-2 strain circulating in Sare Yoba, located in the Kolda region. This paper presents the latest report on sylvatic DENV virus in Africa, and the first detection of circulating sylvatic DENV-2 in Senegal since 2000 [27]. The Kolda

#### **Figure 4.**

*Number of cases per months. The horizontal bar plot shows the number of people that were tested every month from January 2021 to December 2021. The red and blue bars represent positive and negative cases, respectively.*

region, where the contemporary sylvatic DENV-2 strain was identified, shares a border with the Niokolo-Koba National Park, a habitat of monkey species, such as *Papio papio* and *Erythrocebus patas*, which serve as reservoirs for sylvatic DENV [17, 28]. Moreover, experimental studies using surrogate human models and cultured cells have indicated that the emergence of sylvatic DENV in human populations may not have a significant adaptive barrier, possibly due to the virus's opportunistic nature and ability to infect a diverse range of primate species [17].

In the context of utilizing genomic epidemiology to inform health policies, we have developed a user-friendly workflow for obtaining almost complete genome sequences using nanopore sequencing in less than 24 hours. Our generated Maximum Likelihood (ML) tree (**Figure 3**.) indicates that our strain, based on its near-full genome sequence, belongs to the West African DENV-2 sylvatic genotype and is closely related to a strain associated with hemorrhagic DENV found in a tourist who traveled to Guinea-Bissau *via* Senegal in 2009 [29]. This finding suggests that our strain is not related to the DENV-2 cosmopolitan genotype, which caused the most recent DENV-2 epidemic in Senegal [16, 25] highlighting a reemergence of sylvatic DENV-2 in southern Senegal.

The lower number of samples collected from the Kolda region in the 4S network suggests a potential underestimation of the DENV burden in this area. This suspicion was corroborated by the discovery of IgM-positive cases during a seroprevalence study in Senegal in 2021 (Unpublished data). Given the high suspicion of dengue circulation in the southern region, a "One health" approach is urgently needed, encompassing human, nonhuman primates, and vectors. This approach can enhance dengue fever surveillance *via* existing human malaria-like illness surveillance within the 4S network. Real-time genomic surveillance of DENV could be instrumental in discriminating between sylvatic and epidemic strains and improving virus surveillance across the country, with complex transmission dynamics involving both urban and sylvatic DENV cycles. Developing portable mobile platforms for epidemic virus surveillance in resource-poor regions is crucial, and lessons learned from previous epidemics, such as the Ebola outbreak and the SARS-CoV-2 pandemic, will enable better management of future epidemics and improved genomic surveillance of pathogens with epidemic potential.

#### **Acknowledgements**

We would like to thank the all workers at the WHO collaborating center for arboviruses and hemorrhagic fever viruses.

#### **Funding statement**

This work was supported by the Foundation Institut Pasteur de Dakar and the Talent awards earned by Dr. Oumar Faye.

#### **Conflict of interest**

No conflict of interest for any of the authors was declared.

### **Author details**

Idrissa Dieng1 \*, Cheikh Talla2 , Joseph Fauver3 , Mignane Ndiaye1 , Samba Niang Sagne2 , Mamadou Aliou Barry2 , Ousmane Faye1 , Amadou Alpha Sall1 and Oumar Faye1

1 Arbovirus and Viral Hemorrhagic Fever Unit, Institut Pasteur de Dakar, Dakar, Senegal

2 Epidemiology, Clinical Research and Data Science Department, Institut Pasteur de Dakar, Dakar, Senegal

3 Department of Epidemiology, University of Nebraska Medical Center, Omaha, Nebraska, USA

\*Address all correspondence to: idrissa.dieng@pasteur.sn

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Reemergence of Sylvatic Dengue Virus in Southern Senegal, 2021 DOI: http://dx.doi.org/10.5772/intechopen.110900*

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#### **Chapter 4**

## Asymptomatic Dengue and Silent Transmission

*Pavithra Dilakshini Dayananda and B.G.D. Nissanka K. de Silva*

#### **Abstract**

With over 90% of infected proportions being asymptomatic to dengue, their possible contribution to silent transmission has generated much attention in epidemic and non-epidemic settings. The challenges in identifying the true asymptomatic representation, owing to no clinical symptoms, have limited scientific knowledge of the asymptomatic dengue, its viral kinetics, immune mechanisms and underlying protective mechanisms in action. The chapter gives an overview of dengue, and its asymptomatic counterparts. It elaborates on the current knowledge in immunity, and immunopathology in symptomatic cases and provides postulations on possible protective mechanisms responsible for the asymptomatic nature of individuals. The chapter further discusses the importance of identifying the asymptomatic proportion in a community and the challenges in diagnosis. It highlights the major role, that asymptomatic carriers play in silent transmission, and its implications and further discuss the possible measures to minimize the transmission risk.

**Keywords:** dengue, dengue without symptoms, asymptomatic, dengue transmission, silent transmission, transmission risk

#### **1. Introduction**

Dengue is considered the most prevalent arthropod-borne viral disease in the world, causing more than 90 million cases and approximately 40,000 deaths per year [1, 2]. Causative agent- Dengue virus (DENV) is a single-stranded RNA virus of the Genus Flavivirus, which is comprised of 4 closely related, antigenically discrete serotypes, DENV1, DENV2, DENV3 and DENV4. However, in 2013 a 5th DENV serotype (DENV5) also has been reported [3]. DENV is transmitted by *Aedes* mosquitoes, mainly *Aedes aegypti* and *Aedes albopictus*. The virus and its vectors are widespread in over 100 countries worldwide, both tropical and subtropical [4]. Since there is no specific medication other than clinical management, the prevention of the disease relies mainly on vector control, and vaccine development is urgently required. Currently, a live attenuated vaccine, chimeric yellow fever 17D—tetravalent dengue vaccine (CYD-TDV), has been licensed for clinical use in some countries, and many candidate vaccines; including live attenuated vaccines, inactivated vaccines, recombinant subunit vaccines, viral vectored vaccines, and DNA vaccines are still under research and development [5].

Many factors have contributed to the expansion of dengue spread such as population growth, urbanization, inadequate water management, poor waste management, lack of effective mosquito control and increased global travel. Changes in global climatic patterns are believed to have expanded the vector habitat range and resulting increased epidemic activity may have caused an increase in the rate of viral genetic change and the emergence of strains or genotypes with greater epidemic potential [6–8].

Dengue has a wide spectrum of clinical outcomes ranging from asymptomatic to symptomatic; resulting in asymptomatic infections, undifferentiated fevers, Dengue Fever (DF), Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS) [1, 9]; alternatively, they can be classified as dengue with warning signs (DWS), Dengue without warning signs (DWOS) and severe dengue (SD) as suggested by WHO [10]. Each year, 390 million DENV infections occur globally and an estimated 300 million result in asymptomatic/mildly symptomatic [11–14].

Primary Dengue infections are often observed to be asymptomatic and are known to generate immunity to the homologous DENV strain. However, 90% of DWS are known to reportedly occur following a second exposure to a heterologous strain of DENV [15]. It has been observed that sequential or secondary DENV infections are more likely to produce severe diseases [16, 17]. Cross-protection from previous infections and the neutralizing antibody levels also seem to play a major role in determining the level of severity of the disease [18, 19].

#### **2. DWOS; asymptomatic infections**

The incidence of dengue infection has been rising over the last five decades [20] and the majority of infected individuals are known to have no or insufficient symptoms to result in clinical presentation [12, 14]. Mildly symptomatic or subclinical infections are mostly referred to as DENV infections without major symptoms requiring medical attention, while the patients who have virologically or serologically confirmed dengue with no reported or detected symptoms are named dengue 'asymptomatic' patients [12].

Although asymptomatic infections are considered more frequent than symptomatic, the relative number of cases is observed to be vary according to the year of infection, geographical area, the epidemiological context, the immunological status of individuals, and the circulating serotypes and viral strains [21]. The ratios of asymptomatic to symptomatic cases have been shown to vary from 2.1:1 to 13:1 around the world [22] making this change in the proportion of symptomatic to asymptomatic infections, one of the main contributors to the rise in the dengue incidence.

A study carried out in Thailand during 1980–1981 reported a ratio of asymptomatic to symptomatic cases as 6.1:1, while this ratio was refined as 5.5:1 for DENV 1 cases, 4.5:1 for DENV 2 cases and for entirely asymptomatic for DENV4 cases [16]. During the period of 1998–2000, a similar survey in Northern Thailand reported a ratio of 1.1:1 [23]. A study carried out in Central America reported a ratio of 13:1 during the period of 2001–2003 when DENV2 was dominant and a ratio of 6.1 when DENV1 was frequent [24]. It has been reported that the Health authorities in Singapore assumed ratios between 2:1 and 10:1 during the period of 2006–2007 [25]. Studies from Sri Lanka have shown that the asymptomatic to symptomatic ratio was 3.4:8.4 between 2008 and 2010 [22]. In a pediatric dengue cohort study in Nicaragua, a wide variation from 16.5:1 in 2006–2007 [26] to 1.2:1 in 2009–2010 [27] has been shown. All these studies reveal the extensive variation of asymptomatic to

#### *Asymptomatic Dengue and Silent Transmission DOI: http://dx.doi.org/10.5772/intechopen.109791*

symptomatic ratios, where the differences might be attributed to the extrinsic and intrinsic factors of the host and the circulating virus types [24, 28].

Clinically apparent dengue is frequently studied with various research objectives. However, the science behind asymptomatic dengue is inadequately investigated mainly due to the challenges in diagnosing asymptomatic cases on time. Thus, understanding the host factors such as the role of immunity on the lack of clinical symptoms and or the other protective mechanisms for being symptomless has mainly been based on careful investigation of symptomatic cases.

#### **2.1 Dengue; immunity**

Once an immune-susceptible host meets with the infection, an acute, self-limiting febrile systematic syndrome is known to develop usually within initial 4–7 days. This is known to be associated with strong innate and adaptive immune responses [29].

#### *2.1.1 Innate immune response*

At the site of the mosquito bite, Langerhans cells, dermal cells and interstitial dendritic cells of the innate immune system become the initial targets for DENV [29]. The three cell types, monocytes, macrophages, and dendritic cells which are tolerable for DENV infection act as the main phagocytic cells of the innate immune system, responsible for detecting and removing hostile pathogens. These three major phagocytic cells also function as antigen-presenting cells critical for the initiation, expansion, and polarization of adaptive cellular immunity [30]. All these innate immunity mechanisms are triggered immediately upon pathogen invasion and play a significant role in managing pathogenic infection. The killing of target cells is associated with inflammatory cytokine and or chemokine responses [30]. However, DENV has evolved successfully to suppress innate immunity and to infect the host productively using passive and active evasive strategies, which have a negative effect on the subsequent production of antigen-specific adaptive immunity to these viruses [31].

#### *2.1.2 Adaptive immune response (cell-mediated immune response)*

Many studies have shown that the adaptive immune response to DENV has protective as well as detrimental aspects [32]. Dengue-induced immune enhancement plays a major role in the clinical manifestations of dengue disease. The imbalanced and deregulated, cell-mediated immunity is considered as a major component in severe dengue conditions [29]. It is hypothesized that DENV infection of monocytes and macrophages increases T cell activation, leading to the release of cytokines and chemical mediators such as Tumor Necrosis Factors (TNF), Interleukins (IL), Platelet Activating Factors (PAF), complement components and histamines causing increased vascular permeability, plasma leakage, shock and malfunction of the coagulatory system resulting in hemorrhage and shock [33, 34]. In this phenomenon, DENV infection of dendritic cells strongly activates CD4+ and CD8+ T cells which produce a surplus of cytokines, which recruit numerous other cytokines and chemical mediators that further increase the vascular permeability of the host [34, 35].

#### *2.1.3 Adaptive immune response (humoral response)*

Individuals infected with DENV generate serum antibody titers that provide long-term protection against future homotypic infections with the same serotype [32]. Infection with DENV also builds a degree of cross-protective immunity against the other three DENV serotypes by means of heterotypic (cross-reactive) IgG antibodies which usually persist for a duration of several months to a few years [36]. The produced heterotypic antibody titers are known to reduce over long time periods of approximately 4 to 20 years [37]. However, conversely, the homotypic IgG antibody titers are known to increase over time which could be due to the preferential survival of long-lived memory B cells producing homotypic antibodies [37].

#### **2.2 Dengue; immunopathogenesis**

The postulated hypotheses on dengue immunopathogenesis include the antibody enhancement theory, cross-reactive memory T cells activation and the original antigenic sin where all in a way cause either an overproduction or a skewed profile of cytokine release [38, 39].

Antibody-dependent enhancement (ADE); The leading hypothesis is that DHF occurs via ADE of a DENV infection [40–43]. Preexisting heterologous, crossreactive antibodies from a previous infection (or maternal antibodies in infants) recognize and bind to heterologous DENV in a secondary or tertiary infection (primary infection in infants), are unable to neutralize this virus, either because they are non-neutralizing, or due to inadequate avidity or occupancy [41, 44–46]. These non-neutralizing antibody–virus complexes are known to increase the infection of monocytes via their Fc receptors, dramatically increasing viral replication and load, thereby causing DHF. Weak and non-neutralizing cross-reactive antibodies induced from immunodominant B cell epitopes are known to comprise the majority of the humoral immune response to DENV infection [38, 47, 48].

Cross-reactive memory T cells activation and Original antigenic sin; the second hypothesis indicates that there is a highly skewed cellular response to heterologous DENV infection motivated by low affinity, cross-reactive memory CD4+ and CD8+ T cells [49–51]. Cross-reactive T cell epitopes have been identified across the DENV proteome, however, immunodominant CD8+ T cell epitopes in dengue non-structural protein NS3 have been found strongly associated with DHF [15, 52, 53]. The common theme throughout DENV immune enhancement is the concept of "original antigenic sin," which describes the shift in the hierarchy of immunodominance that occurs when previous exposure to cross-reactive antigens alters and inhibits the subsequent immune response to related antigens, either as a new infection or by vaccination [49]. Both humoral and cellular responses are known to be plagued by such misdirected or inappropriate heterotypic immunity [54].

All these mechanisms are known to increase the activation of immune cells, resulting in impaired immune responses or cytokine storms that cause endothelium dysfunction and increase vascular permeability. However, multiple host and viral factors seem to be influencing the determination of the disease severity of DENV infections via favorable and unfavorable interactions thus have triggered much research interest [55].

#### **2.3 DWOS; asymptomatic infections - protective mechanisms**

Fundamental immunological differences in the immune responses associated with symptomatic and asymptomatic infections have been studied [56, 57]. The kinetics of asymptomatic infections are known to differ from the symptomatic infections in the magnitude of the viremia and the rate of clearance [58]. The protective mechanisms that contribute to the lack of clinical manifestations in individuals, that remain asymptomatic

#### *Asymptomatic Dengue and Silent Transmission DOI: http://dx.doi.org/10.5772/intechopen.109791*

or inapparent compared to symptomatic dengue cases have been found interesting and are still being investigated. Epidemiological risk factors such as age, duration between consecutive dengue infections, DENV serotypes of previous infections, concentrations of pre-existing heterotypic neutralizing antibodies, interactions between viral genotype within the serotype and resulting immune responses are known to be associated with these subclinical outcomes after the dengue infection [12, 23, 59–61].

In general, it is regarded that secondary infections are associated with more severe disease due to the phenomenon of ADE and/or cross-reactive T cells [62]. However, post-secondary infections are known to induce different immune responsiveness in susceptible hosts and have also been found to impact upon inapparent rates [63]. Thus, the role of previous infection in perhaps decreasing or increasing the risk of infection causing it inapparent needs to be further investigated [12, 64]. Alexander et al. (2020) have studied the impact of frequent immune boosting; that occurs as a result of frequent disease exposure in dengue-endemic areas, on the fluctuating symptomatic and asymptomatic ratios [28]. It has been reported that antibodies play a greater role than immune cells in heterologous DENV infections [65]. Neutralizing antibodies seem to play a major role in this and it is evident that, the individuals who are previously exposed to DENV, manifest clinical symptoms differently due to the presence of pre-existing neutralizing antibodies resulting in asymptomatic or inapparent dengue status on many occasions. Furthermore, high concentrations of neutralizing antibodies against DENV infection have been frequently observed in asymptomatic individuals [61, 66–68].

Variations in immune reactions to the virus have been reported in dengue asymptomatic and symptomatic patients. In a study carried out by Simon-Loriere et al. (2017), the inflammatory pathways and innate immune responses were found similar in asymptomatic and symptomatic diseases. However, the expression of proteins related to antigen presentation and subsequent T and B cell activation pathways were found differently regulated, independent of the viral load or previous DENV infections. Asymptomatic individuals have been found to have increased T cell responses with feedback regulation compared to symptomatic counterparts [57]. According to his findings, asymptomatic infections seem to be determined by increased activation of the adaptive immune response and properly controlled mechanisms leading to the removal of viral infection without excessive immune activations [57].

Furthermore, apart from immune status, host genetic factors are considered to have an impact on the protective mechanisms in asymptomatic diseases [56], which involves a complex network of genes that are expressed differentially in the asymptomatic or inapparent individuals. A polymorphism in Fc gamma receptors (FcgRIIA) has been found to be associated with inapparent infections compared to symptomatic infections with DF or DHF in the Cuban population [56]. Moreover, according to the studies of [67] a broad down-regulation of host defense response (innate, adaptive, cytokines and matrix metalloprotease) genes in asymptomatic individuals against symptomatic patients. A selective up-regulation of distinct genes which are associated with protection has been observed [66]. However, these observations warrant further investigations in order to correlate their expression with conferring protection against clinical dengue infections.

#### **2.4 DWOS; asymptomatic infections- detection**

Detection of DWOS or asymptomatic infections is known to be challenging. The symptomatic dengue can be clinically suspected based on the symptoms and a confirmatory laboratory diagnosis will provide a definite diagnosis. Detection of asymptomatic cases happens only based on laboratory diagnosis, since there are insufficient or no clinical cues for infection [68].

Direct diagnostic methods such as molecular and antigen-detecting methods are not usually considered convenient to detect asymptomatic infections owing to the shorter period of viremia after the infection. Serological tests such as HAI, ELISA and PRNT have been accepted as suitable methods to detect DWOS and have been frequently applied in detecting asymptomatic dengue cases than the direct diagnostic methods [68]. However, direct methods to detect acute infection and indirect methods; mostly the serological methods and further, mosquito inoculation techniques have also been incorporated in many studies for detecting asymptomatic infection in high-risk cohorts (**Figure 1**) [69–71].

Surveillance studies for DWOS or asymptomatic infections are carried out in the general population over a long period of time with frequent blood sampling and testing [16, 23] and by screening the dengue high-risk groups [71].

#### **2.5 Dengue transmission**

Transmission of DENV among human hosts occurs through horizontal and vertical transmission pathways. In horizontal transmission, viruses are transmitted among individuals of the same generation. Human-to-mosquito transmission is known as the most common mode of horizontal transmission, while transmission through blood transfusion [25, 70, 72–76] and organ transplants [25, 77] have also been infrequently reported. In addition to these transmission modes, a few cases of nosocomial transmission through needle stick injury and mucocutaneous exposure have also been reported [78, 79]. The difficulties in differentiating non-vector transmission from vector or mosquito transmission in dengue-endemic areas could be the result of the observed infrequency of records of these cases [80].

Studies have been carried out to investigate the possible sexual transmission of DENV. So far, cases of DENV in semen [81, 82], and vaginal secretions [83] have been

#### **Figure 1.**

*Schematic diagram illustrating the application of diagnostic tests for the detection of asymptomatic dengue.*

rarely recorded. However, in 2019, two cases of possible sexual transmission were reported in Spain and South Korea [84, 85]. Thus, though plausible, sexual transmission of dengue is considered extremely rare and uncommon in endemic communities [86].

Vertical transmission occurs when the virus is transmitted from mothers to their offspring, through intrapartum transmission [87–89] or transmission at the onset of delivery [80, 87]. Although DENV virus particles have been found in breast milk, the studies are insufficient to conclude the transmission of DENV via breast milk [90], however considering the benefits and immunological protection from breast milk to infants, breastfeeding in DENV-infected mothers are encouraged in dengue -endemic regions [91, 92].

#### *2.5.1 Human to mosquito transmission of DENV*

A susceptible female *Aedes* mosquito acquires a DENV infection after it consumes a blood meal from a dengue viremic person. When viremic blood reaches the mosquito midgut, the extracellular virus binds to undefined receptors on the cellular surface of the midgut epithelium. Once the virus is capable of successfully infecting and replicating in midgut epithelial cells, a new progeny of viruses is shed into the hemocoel, where it can, later on, disseminate and infect secondary tissues, legs, brain and salivary glands [93]. The duration of the viral incubation between the time of ingestion and reaching the salivary glands, where mosquitoes become infectious is known as the extrinsic incubation period (EIP), which is generally considered as 8–12 days [94]. Upon adequate viral replication in the salivary glands, the mosquito becomes a potential vector to transmit DENV to a new host during the next probing or feeding event [93].

The factors influencing the transmission of DENV from humans to mosquitoes include viral, host, vector and environmental aspects. In terms of host factors, viral titer in the human plasma and duration of human infectiousness are considered. The amount of viral titer circulating in the blood of an infected human influences the possibility of a mosquito becoming infected after a blood meal. Mosquito infectious dose, or the viremia in humans that is required to infect 50% of mosquitoes differs between viral serotypes [95]. A dose-response relationship is generally observed with an increasing number of DENV RNA copies [96]. The period between infection and the onset of infectiousness in a human is called the Intrinsic Incubation Period (IIP). The intrinsic incubation period of a human varies, and it is typically considered as 4–7 days [94]. It is estimated that onward transmission results from mosquitoes biting during the pre-symptomatic phase of DENV infections in most cases than, during the post-symptomatic period [14]. Further, it is also reflected that, patients with a high early viremia have a greater probability of having an extended duration of DENV infectiousness. Furthermore, host immune factors [96] and host stimuli for mosquito attraction such as body temperature, body odor, blood type [87, 97], etc. are also known to contribute as host factors for dengue transmission.

As for vectors, diurnal and crepuscular biting behavior of both *Aedes* mosquito species [98], anthrophonic nature, considerable flying span, and highly domesticated nature, especially of the primary vector, *Ae. aegypti* mosquitoes [99] have made them excellent vectors in disease transmission. Mosquito susceptibility to infection and vector competence (VC), which elaborates on mosquito infection, dissemination and onward transmission of the virus, plays a major role in transmission. Relative vector competence of two major vectors *Ae. aegypti* and *Ae. albopictus* have been extensively studied. *Ae. albopictus* are known, more susceptible to midgut infection than *Ae. aegypti*, but the ability to disseminate the virus of *Ae. aegypti* has been found greater

suggesting a greater potential for transmission in nature [100]. The susceptibility for DENV in mosquitoes of different geographical strains has been reported [101, 102] and population-specific differences in the susceptibility with each serotype, have revealed consistent patterns of high and low infection [103]. Further, differential susceptibility by different viral isolates of genotypes within the same serotype in a single geographical population has also been reported [101, 104, 105].

Dengue virus is also known to manipulate the biology and behaviors of the infected host to facilitate virus transmission [93, 106]. Studies on the blood-feeding behavior of DENV-infected mosquitoes have investigated the time duration of probing and feeding [107], transmission efficiency during probing [108], and motivation and avidity to feed [106, 109] and revealed the relationships of such in disease spread.

Environmental factors have been known to play a major role in dengue transmission via mosquito vectors [110]. The temperature has been known to have implications in altering mosquito VC to transmit viruses. The lower temperatures are known to induce slow virus replication and high temperatures are known to induce increased virus replication resulting in reduced EIPs [100, 111]. Changes in the humidity levels are also known to intervene with the vector competency of vector mosquitoes, which affect DENV transmission [110]. Research interest in the factors contributing to DENV mosquito transmission is ongoing and in-depth studies are warranted [93].

#### **2.6 Silent transmission; vector and non-vector transmission**

Studies on vector transmission of DENV from asymptomatic patients are rare and the level of mosquito infectiousness has not been adequately investigated [69]. It was long assumed that people with inapparent and asymptomatic infections fail to infect mosquitoes and have low viremia levels. Many studies have reported lower viremia in asymptomatic infections than those of symptomatic infections but also in detectable levels [58, 69, 112–115].

It has been shown that people with asymptomatic infections have had 100-fold lower infectious doses of viruses to mosquitoes that eventually have resulted in larger viral loads in infected mosquitoes [116]. This was also evident to us in a study carried out in Sri Lanka, where silent transmission from asymptomatic individuals (with no detectable viremia or sometimes no detectable antigen levels), to vector mosquitos (with detectable antigen levels) was observed [71]. A recent study has reported a slower viral decay rate in asymptomatic subjects compared to symptomatic individuals, enabling the asymptomatic cases more available for silent transmission [58]. Furthermore, studies to evaluate mosquito infectivity of asymptomatic subjects have shown a significant increase in mosquito infectiousness among asymptomatic cases than the symptomatic cases (**Figure 2**) [18, 69], postulating that strong immunological response and high cytokine levels during symptomatic illness reduce human infectiousness to mosquitoes in symptomatic dengue cases [69].

Non-vector transmission of DENV via atypical routes such as blood transfusion, organ transplant and intrapartum transmission has been confirmed in many studies, and the possibility of these transmission routes originating from asymptomatic, pre-symptomatic or subclinical cases has also been discussed [12, 73, 117–120]. Furthermore, vertically transmitted dengue in a neonate born to a mother with asymptomatic dengue infection has been reported in a recent case study from Sri Lanka, and instances, where such cases are misdiagnosed owing to no maternal history in asymptomatic mothers have been discussed [121].

*Asymptomatic Dengue and Silent Transmission DOI: http://dx.doi.org/10.5772/intechopen.109791*

**Figure 2.** *Schematic diagram illustrating the increasing transmission risk towards the asymptomatic proportion of an infected community.*

According to the modeling analysis of Bosh et al., (2018), it has been suggested that inapparent infections contribute appreciably to DENV transmission and its disease burden [14]. Further, their finding that approximately one-quarter of an individual's infectiousness occurs prior to symptom onset, supports the hypothesis that a large proportion of human to-mosquito transmission is silent [14]. Collectively, these evidences show that asymptomatic cases play a major role in silent transmission, having a high transmission risk compared to symptomatic cases (**Figure 2**). Furthermore, the fact that the vector- host contact is considerably high in asymptomatic carriers through their daily routines compared to symptomatic cases, who will be hospitalized or less accessible should also be accounted with great concern. In addition, human mobility is also known to play a key role in the spread [122, 123], thus silent transmission of dengue via undisrupted daily routings of these asymptomatic or mildly symptomatic carriers can be identified as a key factor contributing to the dengue spread than the symptomatic cases [69, 100] (**Figure 2**).

#### **2.7 Seroprevalence and risk of antibody-dependent enhancement**

Relatively high dengue seroprevalence among the dengue endemic communities around the world has been reported [13, 24, 124–129]. Comparative to the number of confirmed dengue cases, an increased level of dengue infection suggested by high IgG seropositivity in endemic areas, has revealed a vast majority of DENV infections [128]. Attributing to the fact that the majority of dengue infections in these communities are either asymptomatic or inapparent [11, 14, 16, 23, 65].

As a consequence of this, a considerable proportion of the population who are immune to a circulating dengue serotype/strain after an epidemic will be created. Co-circulation of several dengue serotypes in dengue-endemic areas has been reported [129, 130]. Worsening the situation, the prolonged seroprevalence in symptomatic and asymptomatic individuals has also been observed in studies [13]. Thus, this proportion would be at risk of developing ADE or severe dengue in a subsequent epidemic of a differing dengue serotype with non-neutralizing antibodies or neutralizing antibodies at sub-neutralizing levels (**Figure 3**).

Furthermore, the transmission of heterogeneous anti-dengue antibodies from symptomatic or asymptomatic cases through blood transfusion or organ transplant, and transmission of maternal antibodies to infants has also been suggested to enhance

#### **Figure 3.**

*Schematic diagram depicting the high seroprevalence of dengue virus in dengue-endemic communities and the risk of developing antibody-dependent enhancement during subsequent infections.*

the viral infectivity and virulence in recipients who will later be exposed to a heterotypic DENV infection [131].

The global incidence of DHF/DSS has increased more than 500-fold in recent years [11]. And the risk of dengue virus or its antibodies which can be transmitted through such different passive modes of transmission has been identified as a major counterpart.

#### **2.8 Prevention; a way forward**

Prevention from silent transmission through mosquito vectors can only be achieved by vector control, in a setting where asymptomatic carriers can only be identified by certain laboratory identification techniques. However, the routing fogging and insecticide spraying practices just after a case report (peri-domestic space spraying) can be taken as an initial step to reduce the risk of transmission from asymptomatic carriers. Although many studies have suggested the importance of screening the populations for DENV, and dengue seroprevalence, no available efficient measures and or diagnostic services for such events prevail in many dengue-endemic countries [75].

However, there is a need to incorporate integrated approaches including increasing awareness among the community, establishing routine diagnostic methods for screening asymptomatic carriers and incorporating preventive measures to reduce the exposure, which will eventually help in reducing the dengue burden [75].

Many endemic countries have identified the risk of transfusion-associated transmission from asymptomatic donors, and have adopted policies where they recommend screening of blood products. The positive blood donors will be deferred for periods depending on the endemicity of the region. Similarly, transplant guidelines in *Asymptomatic Dengue and Silent Transmission DOI: http://dx.doi.org/10.5772/intechopen.109791*

some countries have recommended dengue screening prior to transplantation and a specific deferral period before taking up for transplant surgery if the donor or recipient is found positive for dengue.

Vaccines and herd immunity; though seems like the only promising solution, limited knowledge of immune responses against dengue infection, lack of human or animal model of disease, and suboptimal assay strategies to detect immune responses after infection or vaccination, which are some barriers to the vaccine and drug development. Furthermore, in addition to the protection against symptomatic infection, it is also important to assess protection against asymptomatic infection.

#### **3. Conclusion**

Asymptomatic or inapparent dengue infections provide a fundamental link in the chain of disease transmission in dengue-endemic communities. The knowledge gap in understanding the viral kinetics of asymptomatic individuals along with their immunorespnoses must be urgently fulfilled and investigative studies on such should be encouraged. Understanding the presence and the prevalence of asymptomatic to symptomatic proportion of a community enables a glimpse of the targeted population and helps in introducing disease management strategies. The chapter highlights the increased transmission risk towards the asymptomatic carriers of the community, attributed to the increased vector-human contact, human mobility and mosquito infectiousness. All precautions must be taken to reduce dengue transmission in a community via vector and non-vector routes. Furthermore, the seroprevalence of a community must be routinely monitored and the vaccine efficacy in such settings depending on the endemicity, should be closely evaluated.

#### **Acknowledgements**

We appreciate the support of Dr. Dulan Jayasekara, for designing the figures for us.

#### **Conflict of interest**

The authors declare no conflict of interest.

#### **Author details**

Pavithra Dilakshini Dayananda1 and B.G.D. Nissanka K. de Silva2 \*

1 Genetics and Molecular Biology Unit, Faculty of Applied Sciences, University of Sri Jayewardenepura, Nugegoda, Sri Lanka

2 Department of Zoology, Faculty of Applied Sciences, University of Sri Jayewardenepura, Nugegoda, Sri Lanka

\*Address all correspondence to: nissanka@sci.sjp.ac.lk

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Asymptomatic Dengue and Silent Transmission DOI: http://dx.doi.org/10.5772/intechopen.109791*

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#### **Chapter 5**

## Dengue Virus Surveillance and Blood Safety: A One Health Perspective

*Festus Mulakoli, George Gachara, Eric Ndombi and Samoel Khamadi*

#### **Abstract**

The provision of blood products to save a life is a noble undertaking for any organization tasked with the duty. In addition to saving millions of lives, blood products pose health risks associated with adverse events. Much has been done to mitigate these challenges, but emerging new infectious diseases pose a public health challenge to both the safety of blood and its availability. The dengue virus an arbovirus is one such virus that is endemic in tropical and subtropical countries. The data emerging from the published papers show that dengue could be a major threat to blood safety and availability in the future. To address these threats, a collaborative approach through one health system is the only avenue to provide a last solution. One health has been implemented as a strategy to mitigate zoonotic diseases and its results are very impressive. This piece of work is a fraction of our larger project that aims to address threats to the dengue virus and blood safety in Kenya and the rest of Africa. In conclusion, adopting one health in the fight against the dengue virus in blood safety will be the best approach to ensure a safer supply of blood products.

**Keywords:** dengue virus, blood safety, surveillance, one health

#### **1. Introduction**

Dengue fever is a mosquito-borne disease endemic in the tropical and subtropical regions of the world. The highest burden of diseases is reported in the Asian and South American regions [1]. The virus has four serotypes (DENV 1–4) that are antigenically different, but with variations in their immunological response. The dengue virus inhabited primates before jumping into the human population. It is one of the main arboviruses associated with frequent disease outbreaks reported annually in endemic regions [2]. The rapid spread of the dengue virus has had a negative impact on blood safety and availability in endemic areas. For example, there is a reduction in the number of suitable donors during DENV outbreaks, as shown in studies conducted in India, China and Brazil. Affected countries have different strategies available to mitigate these threats, but with minimal success. The challenge has always been the lack of collaboration between entities involved in surveillance activities. The most critical limitation is the inability to share critical surveillance information on emerging disease patterns [3]. From an expert point of view, we believe that the adoption of one health in disease surveillance would be the best avenue to guarantee a safer blood supply.

One health, as is known, is a multidisciplinary platform where experts in human health, animal health, and environmental health work collaboratively to combat both human and animal diseases. These synergistic efforts put blood transfusion services in a better position to safeguard their blood supply in an era of the re-emergence of the dengue virus [4]. The Manhattan Principles, which outline relationships between infectious diseases, the environment, human health, and economic development activities, established the phrase "One Health" in 2003 [5]. This was after the outbreak of Ebola virus disease (EVD), a Filoviridae virus, in West Africa after the death of the great apes. Since then, high-level interest and acceptance of One Health initiatives have grown around the world [6]. The concept of One Health was adopted to allow the sharing of information and to foster collaboration between different sectors. It is a multidisciplinary initiative in which people working in different sectors within their countries, continents, and global regions come together to solve a common public health problem. The connectivity between humans, animals, and their ecosystems is agreed to play a significant role in the spread of infectious diseases [7–10]. This book chapter is a fraction of my Ph.D. project that seeks to highlight and evaluate the importance of adopting one health disease surveillance approach to safeguard blood supplies across the world. One aspect of one-health is helping different experts from different fields share information that can detect and suppress diseases upstream before they cause human disease [11].

#### **2. Current evidence of transfusion-transmitted dengue**

Transfusion-transmitted dengue (TTD) is a growing concern for many transfusion services in tropical and sub-tropical countries. These countries have experienced frequent outbreaks of dengue in the last ten years. The increasing number of dengue incidents increases the likelihood that blood components manufactured during dengue outbreaks could be infectious [12, 13]. The first documented cases of TTD in the literature were reported in two studies in Hong Kong and Singapore in 2008 and 2012, respectively. The cases involved blood recipients who received blood transfusions from asymptomatic blood donors. On evaluation of the transfused blood, the serotype detected in blood recipients was the same as the serotype present in blood donors. This became the first evidence of dengue transmitted by blood transfusions [14, 15]. Irrespective of this evidence, little was done to communicate this information to alert other regions where the dengue virus is endemic. With this evidence, it was important for all blood transfusion services in regions with frequent outbreaks of dengue virus to have taken urgent steps to secure their blood supply. This is a gap that needs to be filled by integrating one-health into our mitigation efforts to protect blood supply and availability.

In regions with widespread outbreaks of the dengue virus, the probability of receiving blood from asymptomatic donors is high and is easily missed by symptombased exclusion criteria [16]. The high number of asymptomatic blood donors is

#### *Dengue Virus Surveillance and Blood Safety: A One Health Perspective DOI: http://dx.doi.org/10.5772/intechopen.109413*

the principal cause of the rising incidence of reported TT-DENV cases in dengueendemic regions [17–20]. Asymptomatic individuals have a higher viral load on their peripheral blood circulation, but they do not exhibit signs and symptoms associated with dengue fever. This makes it difficult for an experienced blood donor recruiter to exclude such risky donors. Things have also been made worse by a regional variation in the incidence rate of dengue viremia from voluntary blood donors. The case at this point is Brazil with 0.04–0.81%, Puerto Rico with 0.02–0.19%, and Honduras with 0.3% [21–24]. Data gathered a few years ago depict a viral viremia that can last up to 24 hours before the manifestation of any clinical symptoms [25]. Unfortunately, minimal information is available during outbreaks, making it difficult for BTS to select donors during recruitment [26].

The dengue virus is rapidly spreading to new areas and significant outbreaks are becoming more common. **Figure 1** illustrates the global region with documented cases of dengue viral markers detected in healthy blood donors. The highest burden of dengue among eligible blood donors is seen in Brazil and India [17, 20, 27–35]. The burden from other regions is lower, probably masked by a lack of testing and surveillance initiatives. The susceptibility to the virus has recently changed as individuals targeted for donation have become vulnerable. Most potential blood donors would be rejected if they were subjected to pre-donation screening [36]. This has affected the blood supply because more blood donors are deferred from donating blood due to dengue infection or exposure. Blood transfusions from asymptomatic viremic donors will also increase the probability of transmission. Although effective disease reduction and dengue screening techniques have been implemented in developed countries, the initiative is costly for low-income countries. As the number of patients with DHF/DSS increases, so will the demand for blood products such as platelet rich plasma [37–39].

**Figure 1.** *Regions with documented cases of dengue virus among blood donors.*

#### **3. Dengue virus and blood safety: one health perspective**

Past outbreaks of emerging infectious diseases have highlighted the close relationship between human and animal health and their environment. A broader understanding of health and disease dynamics demands an integrated approach, which can only be achieved through a convergence of humans, domestic animals, wildlife, and the ecosystem through one health magnifying lens [40–43]. Many include the extinction of some animal species, environmental degradation, environmental pollution, jumping microbial species, and global warming. These are examples of natural drivers of nature that have positively or negatively impacted life on planet Earth and its ecosystems. The emergence and reemergence of infectious diseases endanger not only humans and their livelihood, but other biospheres that support life on earth [44]. Holistic care for our environment and the future of our health has a close connection with what happens in the ecosystem we live in. To safeguard the blood supply that supports the general health of human beings, an interdisciplinary and multi-sectoral approach is paramount. In all measures to protect blood recipients through surveillance systems, disease monitoring, vector control, and environmental conservation, no effort is directed toward an integrated approach through one health system [45].

One Health-One World perception advocates for well-coordinated approaches that will enable a better understanding and management of a complicated health crisis [46, 47]. The only way to solve such problems is to initiate a strategy that integrates all activities in human health, animal health, and environmental preservation into a single system. Different professional leaders and decision-making organs come together collectively to establish an interdisciplinary approach to the treatment of health issues in different communities [48]. Other stakeholders, including global organizations, national governments, and the research community, apply the One-Health approach as a holistic mechanism to combat the spread of infectious diseases. This is one of the best platforms for addressing complex health issues such as emerging and reemerging infectious diseases in blood transfusions [49]. The One-Health and One-World principle focuses on improving our disease surveillance systems in terms of epidemiological trends of diseases and their impact on our economy. It is hoped that one health approach will improve our knowledge of health issues and provide an avenue to develop interventions that are pocket friendly to most counties. A variety of technical, organizational, and sociological factors are an impediment to the long-term implementation of One Health surveillance [50].

In the current world, the world has become a global village and infectious diseases spread rapidly from one nation to another. This is promoted by the interconnectivity of countries through modern transport networks and human movements. This uncomplicated mobility of people around the world shows clearly that no single professional discipline or sector has enough knowledge and resources to prevent the emergence or resurgence of diseases in blood transfusion [51]. The only way to face the future is to eliminate barriers between organizations, individuals, specialities, and sectors. The world requires innovation and collaboration between various sectors to mitigate the frequent threats to human health, livestock health, wildlife, and the integrity of our ecosystem. Current threats and future problems cannot be solved with outdated interventions. The world has become a "One World, One Health" era, and we must develop new mechanisms to handle these threats. Forecasting future threats and working collaboratively in a multidisciplinary approach is the only way to overcome the challenges that arise from emerging infectious diseases in blood transfusions. **Figure 2** is an example of a probable approach through one health that

*Dengue Virus Surveillance and Blood Safety: A One Health Perspective DOI: http://dx.doi.org/10.5772/intechopen.109413*

**Figure 2.**

*One health perspective on protecting the blood supply against the dengue virus and other emerging infectious diseases.*

will help blood banks keep pace with new threats. A similar approach to address challenges in the fight against diseases in the general human population and in the animal population has yielded good results [52, 53].

#### **3.1 Human disease surveillance**

#### *3.1.1 Epidemiological surveillance*

A robust surveillance structure is critical for disease prevention for any country in an era full of emerging disease outbreaks. Communication of early warning signs through one health surveillance system helps in preparedness for blood transfusion services. Traditionally, surveillance system models are structured at three levels: event-based, active, and passive surveillance systems [54]. All three systems are applied based on the prevailing circumstances, but with various limitations. One health is the best link to connect all three to address emerging infectious diseases in blood transfusion. Identification of new threats and the ability to share information on risks from passive surveillance would help secure our blood supplies [55]. However, for diagnostic and clinical laboratories, all three surveillance components will be essential to generate surveillance data on viral, bacterial, and parasitic diseases. The basis of disease surveillance is not to investigate all agents, but to investigate data on disease patterns across the world. From a personal understanding, the three surveillance strategies seem inadequate, but they are better than nothing. When used effectively and integrated into our disease mitigation programs, they help predict future disease outbreaks [56].

An active surveillance system is one of the most effective methods used in China to monitor the circulation of infectious diseases in the endemic region of the disease of the disease [57]. Health officials monitor dengue transmission at the local level and can accurately pinpoint the exact pattern of the disease in their locality. These generate data on the serotypes of viruses that are circulating, the burden of the disease, and the complications associated with dengue infection at any time. The strategy here is to have dengue virus surveillance integrated into routine diagnostic laboratory operation [58]. When properly managed, disease surveillance systems can predict and provide early warning before disease outbreaks. However, due to resource constraints, this is not achievable in low-middle-income countries. Additional active surveillance integrated into BTS will increase the overall cost of blood transfusions [59, 60].

With this approach, disease epidemics can be easily predicted and necessary measures are taken to combat the situation. This initiative-taking surveillance system must have at least two elements focusing on the epidemic or interepidemic period. A sentinel site/physician collaboration, a fever vigilant structure that uses peripheral health workers, and a sentinel hospital system are some types of active surveillance systems [61–63]. The main objective of this surveillance mechanism is to assess and detect disease patterns before there is a rise during the interepidemic period. However, once an epidemic occurs, the focus should be on reducing the spread of infectious diseases. Surveillance strategies must be redesigned and directed toward a contextualized region [64].

Countries with evidence of the presence of dengue virus should have disease surveillance mechanisms as part of their disease prevention intervention. They should also be required to develop a legal framework to recognize dengue as a reportable infectious disease [65–68]. The best place to have this approach would be within the BTS, provided that there are standardized case definitions and a formalized mandated reporting system. Although passive systems are less accurate in prediction and have low specificity because cases are not laboratory confirmed, this can be improved by having them integrated into blood transfusion services. Blood transfusion centers are strategically located and may serve a useful purpose in monitoring and monitoring dengue circulation within a community [69].

The clinical continuum of dengue virus infection illnesses ranges from asymptomatic to the most severe form of DHF/DSS. Clinically, it is usually a difficult task to differentiate between fevers associated with DF and other infectious diseases. As a result, laboratory diagnosis should supplement surveillance. Reporting of dengue disease is best when clinical diagnosis, epidemiological data, and laboratory confirmation are combined [70, 71].

Case reports should be requested from all hospitals, clinics, private physician offices, and other facilities that treat the susceptible population as part of passive surveillance [72]. Because not all clinical cases are accurately detected during low transmission, passive surveillance is insensitive even when required by law [73, 74]. Several individuals who suffer from a mild, non-specific viral condition self-medicate at home without consulting a doctor. Under a passive surveillance approach, considerable transmission has already occurred and may have reached its peak by the time doctors identify and record dengue cases [75].

However, passive monitoring for DF/DHF has two drawbacks. The reporting criteria are uneven, to begin with. Although some nations only report DHF, others also report DF. Second, when reporting instances, the CASE definitions are not always followed. These problems lead to under- and over-reporting, making monitoring systems less effective [76].

Last but not least, the purpose of event-based monitoring is to investigate a strange health occurrence, including fevers with unexplained causes and clustering of cases [77]. Unlike the conventional surveillance system, event-based surveillance should be an investigation carried out by an epidemiological unit with the support of a microbiologist, an entomologist and other personnel pertinent to the particular event. This will allow the implementation of interventions to stop the further spread of the infection [78].

#### **3.2 Environmental surveillance**

#### *3.2.1 Entomological surveillance*

To prioritize areas and seasons for mosquito control, it is essential to carry out regular surveillance of Aedes aegypti to identify its distribution, population density, major larval habitats, spatial and temporal risk factors related to dengue transmission and susceptibility or insecticide resistance levels [79]. This information will make it possible to choose and use the most effective mosquito control methods while also keeping track of their effectiveness. Adult and larval populations can be found and tracked using a variety of techniques. Based on monitoring goals, infestation levels, and resource availability, the best techniques [80] are selected. Information about such activities will be of help if shared with blood transfusion services. A risk mitigation strategy that is helpful for transfusion services by providing adequate time to make risk-based decisions.

The Breateau index is the most insightful indicator that shows a connection between homes and positive containers but does not account for container productivity [81]. However, it is desirable to profile larval habitat characteristics while collecting basic information for the Breateau index by simultaneously logging the relative abundance of the different container types, either as potential or actual mosquito production sites, for example, the number of positive drums per 100 houses, number of positive tires per 100 houses [82]. These facts are crucial for concentrating efforts on managing or eliminating the most typical habitats. The rate at which newly emerging adults from different container types contribute to the adult mosquito population can vary significantly. Counting all pupa in each container allows one to estimate the relative adult production [83].

To assess the relative significance of larval habitats, the Pupal index can be broken down into "useful", "nonessential", and "natural" containers or by particular habitat types such as tires, flower vases, drums, and clay pots [84, 85]. This method may not be used for routine monitoring or in every Aedes aegypti population survey because of the practical challenges and labor-intensive efforts needed to achieve pupal counts, especially from large containers. Instead, it can be saved for special studies or used twice in each locality, once during the wet season and once during the dry season, to identify the most productive containers. For practical purposes, the Pupal index has been the most widely used strategy [84, 86]. The basis for making the greatest use of a few resources can be laid by identifying the classes of containers in the neighborhood that have the highest rates of adult emergence. These classes can then be selectively targeted for source reduction or other mosquito control treatments [87, 88]. The pupal/ demographic survey is a technique to determine the most important epidemiological container types. Unlike conventional indices previously discussed, pupal/demographic surveys count all pupae in various types of containers in each community [89, 90].

In real practice, a pupal/demographic survey comprises going to a selection of randomly chosen homes. The number of occupants in the house is noted. With the homeowner's consent, the field employees search for the contents of each water-filled container at each place, strain the contents through a sieve, and then resuspend the sieved contents in a small amount of clean water in a white enamel or plastic pan. Put every pupa in a vial with a label. Large containers provide a great challenge in pupal/ demographic surveys, as it is difficult to identify the precise number of pupae in them [86, 90, 91].

Sweep-net techniques with calibration factors have been devised in such circumstances to estimate the overall quantity of pupae in particular types of containers. When returning to the lab, the contents of each vial are moved to tiny cups and covered with mosquito nets fastened with a rubber band if there are any other species except Aedes aegypti in the region. They are maintained until adult emergence, when taxonomic identification and counting can be performed [92]. The collection of demographic data allows us to calculate the ratio of pupae, as reported by Ha and León [85] (a proxy for adult mosquitoes) to people in the community. There is increasing evidence that, when combined with other epidemiological parameters, such as seroconversion rates and temperature specific to dengue serotypes, it is possible to determine the level of mosquito control required in a specific location to prevent virus transmission. This is still an important area of research that needs to be validated. Procedures for sampling adult mosquitoes can provide valuable information for studies on seasonal population patterns, transmission dynamics, transmission risk, and evaluation of adulticide interventions [93].

Planning and evaluating control measures requires knowledge of the sensitivity of Aedes aegypti pesticides. The status of resistance in a population must be carefully monitored in several representative sentinel sites based on the history of insecticide usage and eco-geographical situations to ensure that timely and appropriate decisions on matters like the use of alternative insecticides or the change of control strategies are made [94, 95]. Over the past 40 years, chemicals have been routinely used to prevent mosquitoes and other insects from dispersing illnesses that are crucial to public health. DDT, temephos, malathion, fenthion, permethrin, propoxur, and fenitrothion are only a few of the insecticides widely used that Aedes aegypti and other dengue mosquitoes have become resistant to. The operational influence of resistance on dengue control has not yet been extensively evaluated [96–98]. In countries where DDT resistance has been pervasive, pyrethroid compound precipitated resistance, which is increasingly employed for space spray, is a problem. The voltage-gated sodium channel and mutations in the Kdr gene have been related to resistance to DDT and pyrethroid insecticides in Aedes aegypti because both types of pesticides act at the same target location [99]. Therefore, it is recommended to obtain baseline information on insecticide susceptibility before starting insecticide control operations and to check the susceptibility levels of mosquito larvae or adults [100]. WHO kits to assess the susceptibility of adults and larvae mosquitoes continue to be the accepted approach to assess the susceptibility of Aedes populations. Techniques for analyzing an individual mosquito's biochemistry and immune system have also been created and are currently being used in the field [101].

Integrated community-oriented pest control solutions need the routine monitoring of additional metrics to assess elements such as the number and spread of mosquitoes. These include things such as population density and distribution, settlement traits, land tenure situations, dwelling types, and educational attainment [98, 102, 103]. The planning and evaluation of dengue risk must monitor these characteristics. It is also crucial to understand how home water storage and solid waste disposal techniques have changed over time, as well as how water supply services are distributed, their quality, and their dependability.

#### *Dengue Virus Surveillance and Blood Safety: A One Health Perspective DOI: http://dx.doi.org/10.5772/intechopen.109413*

Weather data are also crucial in monitoring dengue activities within endemic regions. This information helps to structure epidemic intervention strategies and the planning of focused source reduction and management operations [104]. Some of these data sets are produced by the healthcare industry, so it may be necessary to use additional data sources. For program management, annual or even less frequent updates are generally sufficient. If meteorological data, in particular rainfall patterns, humidity, and temperature, are to be predictive in identifying seasonal trends in mosquito populations and their short-term changes, a more frequent study is necessary [105, 106].

#### *3.2.2 Why one health approach?*

One health intervention is a system-thinking approach that helps low- and middleincome countries address threats from dengue and emerging viral diseases in blood transfusion. With limited resources to support their healthcare systems, affected countries will allocate financial resources appropriately where they are needed most. Proper allocation of resources within the different sectors would help most countries deal with collective threats from the dengue virus to blood safety. The avenues available are the establishment of a common laboratory testing facility and an information sharing platform for all sectors involved in dengue surveillance in endemic regions [107, 108].

One health program is an asset to struggling countries that will help them use resources properly to safeguard their blood supply. The challenges facing most blood banks around the world are the lack of adequate financial resources and technology to conduct additional testing of their testing algorithms. The only way to properly use resources is to integrate a system-thinking approach through one health. This approach has had a positive impact on other interventions where one health was implemented to address disease surveillance [109].

Dealing with a complex health problem is a big investment that is not sustainable if only one sector approaches it. Different sectors working collaboratively to address threats to blood safety from emerging infectious diseases provide a sustainable intervention. One Health offers a platform through which different players in blood safety can work with a common goal in mind [110].

Improvement and well-coordination of health systems through one health system is easier than in different sectors working separately. Having a common well-coordinated approach is more impactful and easier to monitor compared to having different players working separately [111–113]. A well-coordinated communication channel between blood transfusion services and other sectors involved in disease surveillance will ease the threats of emerging infectious diseases.

#### **4. Conclusions**

In summary, emerging infectious diseases such as the dengue virus threaten the safety of blood transfusions in endemic regions. Necessary measures are required to protect blood recipients from emerging infectious diseases. One Health provides a platform through which various stakeholders, working collaboratively, can ensure that information is available on disease trends in a particular geographic region. Integrating one health into the main disease surveillance system will save most countries millions of dollars in terms of preparation within the blood transfusion sector.

#### **Acknowledgements**

We want to thank our colleagues both at Aga Khan University and Kenyatta University for their moral support during the writing process of this book chapter. Above all, we also thank our Almighty God for granting us good health and energy during the writing process. Finally, a big thank you to my babies Victoria and Fortune for giving me reasons to pursue my scholarly work.

### **Conflict of interest**

The three authors declare that they have no conflict of interest.

### **Author details**

Festus Mulakoli1,2\*, George Gachara3 , Eric Ndombi4 and Samoel Khamadi5

1 Aga Khan University, Nairobi, Kenya


\*Address all correspondence to: mulakolifesto@gmail.com

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Section 2
