**1. Introduction**

Dengue is a single systematic and dynamic disease that includes severe and non-severe clinical manifestations [1]. It is caused by any of the four dengue virus serotypes and it is transmitted by *Aedes* mosquito bites, being the main vector *Aedes aegypti* [1]*.* Dengue can be maintained in an urban cycle which involves humans and it is a serious health problem worldwide [1]. For the past decades, this disease has been spread alarmingly due to different factors like climate change, migration of people, tourism, lack of access to basic services, etc. [1, 2]. Not only does it affect a large portion of the world's population but also it offers lessons in health sector, research and epidemiology which must be skilled to help in better understanding of the cycle of this disease, set out control strategies and lead the way to future investigations. Thus, in this chapter we are going to discuss some of the main lessons learnt throughout work experiences with this disease and we will learn new strategies designed for studies, assessment and control.

## **2. Dissemination of the disease in urban areas and transmission mechanisms**

Dengue is the most important and common arbovirus in more than 100 countries [1]. This disease is caused by one of the four serotypes of dengue virus (DENV), more than one dengue serotype can be found in many geographical areas (phenomenon called hyperendemicity) [1]. Outbreaks of this disease have been

reported in America, Africa, Mid-west, Asia and the Pacific islands [2]. Nearly 3 billion people (40% of world population) are at risk in areas where dengue occurs, and about 70% of the population at risk are in South East Asia and Western Pacific region [2]. About 400 million people are infected with dengue annually, of which 100 million people are sick and 22,000 die of severe dengue [3]. A virus, a vector and a sensitive population must be in the same geographic area for a dengue onset outbreak [1]. Travelers contribute to dengue dissemination to non-endemic areas but they may also serve as sentinels for warning dissemination. Some studies indicate that dengue represents about 2% of the diseases from travelers returning to from endemic areas [4]. Based on GeoSentinel, a data-collection network between 1997 and 2006, dengue was imported from South-east Asia (51%), South Central Asia (17%), Latin America (15%), the Caribbean (9%), parts of Africa (5%) and Oceania (2%) [4]. The number of febrile travelers returning from the tropics and sub-tropical areas being diagnosed with dengue has increased from 2% in the 1990s to 16% by 2005 [4]. A study of paedriatic travelers in 19 countries reported dengue and typhoid fever as the most often febrile diseases in children returning from tropical regions and sub-Saharan Africa [4]. *Aedes aegypti* vector can be disseminated relatively easy in urban areas because of its strong anthropophilic habits, its biological features like egg resistance to desiccation, its permanence within and not away from the urban centers, and the search for water with low load of organic matter for its oviposition making its arrival in rural areas, where the temperature enables its replication, relatively simple; transform cemeteries, tire repair shop, bus terminals, etc. in critical points of infestation where the vector surveillance must be carried out [5]. The virus can reach new areas where cases of symptomatic and asymptomatic persons or cases of people's incubation period of the disease have not been reported. Around three-quarters of dengue infections presented each year are clinically inapparent, the asymptomatic ones were considered dead-end hosts because they do not produce high enough viremia to infect mosquitoes [6]. Some studies provide evidence that despite a low level of viremia, dengue asymptomatic persons were capable of transmitting the disease to mosquitoes and potentially enabling a high virus transmission. Since it has no symptoms, they could continue in their day-to-day work and be exposed to mosquito bites [6]. The virus can also be spread through infected mosquitoes so that once the mosquito is infected and the extrinsic incubation period is passed, it can be a lifelong carrier of the virus which is about 2 weeks or a month. The interruption of dengue transmission was possible in the 60s and at the beginning of the 70s as a result of an *Aedes aegypti* eradication. The lack of surveillance and vector control followed outbreaks in the Caribbean, Central America and South America [1]. From this experience, it is considered that vector control and epidemiological services detecting and studying dengue cases have to work together and maintain a constant vigilance [1]. The monitoring service should be capable of making the difference between a seasonal and/or temporary increase and increases in the number of cases resulting from a dengue outbreak so that tools of epidemiology as the endemic channel are highly important. If the number of cases reported is higher in two standard deviations above the endemic channel in monthly or weekly notifications, a warning of dengue is produced [1, 7]. However, the lack of notifications continues to be one of the most significant problems in order to prevent and control this disease in many countries as well as in the western Pacific region [1]. The Geographic Information Systems (GIS) allows the analysis of this information on the geographical reference basis in space and time. This type of systems is important for vector-borne disease surveillance and vector control strategy planning [8]. DENV can be transmitted to humans through the bite of female mosquitoes of the *Aedes aegypti*. Other dengue transmission mechanism

**19**

*Lessons Learned and Recent Advances in Dengue Research*

is the perinatal transmission and it occurs when a mother is infected near the childbirth so that the infection can be transmitted through microtransfusion when a placental abruption occurs or during delivery when the mother's blood gets in contact with the newborn's mucosal. Dengue in pregnancy is related to premature delivery, fetal distress in labour, intrauterine death and miscarriages. DENV can also be transmitted through breast milk or exposure to blood, organs or infected tissues like bone marrow [9]. In a study carried out at the Brazilian blood center from February to June in 2012, donors tested positive for DENV-3 and DENV-4 were found and 42 units of PCR tested positive were transfused in 35 recipients. Of these findings, 16 units testing positive were transfused in 16 sensitive recipients in which 5 possible cases transmitted by transfusion (TT) were found, 1 case was considered as a possible TT, and 10 of them were not transmitted. However, no significant differences were found between symptoms and mortality in cases and controls [10].

**3. Dengue virus serotypes and genotypes and its relation to clinical cases**

The evolution of molecular biology and phylogenetic analysis has enabled molecular epidemiology studies binding DENV-phylogenetic analysis which was found in different geographic areas within a certain period of time and clinical and epidemiological data in order to establish a relation to genotypes and lineages which are found with other circulating strains as well as to identify the origin and the transmission route, the severity of the disease, etc. There are four related DENV serotypes but antigenically different DENV-1, DENV-2, DENV-3, DENV-4 and each of them generates an immune response to the infection. The nucleotide sequences show 63–68% homology within the DENV group in comparison with 44% between DENV and Yellow Fever virus (YFV), and 51% between DENV and West Nile virus (WNV), and it shares a minor homology at 80% at a level of amino acids [11]. Previous studies based on partial (prM/E), partial or complete E gene; or complete

genomic sequences recognized distinct DENV genotypes [12] (**Table 1**).

The genotypes may present different lineages or clades. The genetic changes in the virus are caused by mutations or the introduction of a new variant from other region, thus genotyping of strain virus is used to identify the epidemic outbreak source and spread [12]. Some dengue genotypes are related to a higher virulence. DENV-2 and DENV-3 Asian genotypes are associated with severe infections [1]. In South East Asia, dengue hemorrhagic fever (DHF) and/or dengue shock syndrome (DSS) outbreaks are caused by DENV-2 southeast Asian genotype strain, meanwhile epidemics caused by DENV-2 in Latin America presents solely dengue fever (DF) in most cases. The DENV-2 genotypes circulating in the United States seem to be less virulent. Because of the introduction of the South East Asian genotype virulent, the number of cases of DHF and DSS in America has increased [1, 11]. It is thought that an infection with DENV serotype provides lifelong immunity against the same serotype infection and short-term protection against infection by a 2 or 3 month-heterologous serotype [1, 11]. Some studies contradict the hypothesis that has been accepted until now. In 2010–2011 a study in DENV-2 American/Asian genotype outbreak was conducted in Iquitos, Peru. It was carried out 15 years after the first DENV-2 American genotype in that region. The results on the study showed that protection against homologous DENV-2 may be incomplete [13]. In another study carried out in Peru, it was found that the antibodies of a primary infection against DENV-1 neutralized more efficiently in American DENV-2 than in Asian DENV-2. It is believed that this cross-protective immunity is not so strong to inhibit viremia but it may contribute to reduce DENV-2 infection

*DOI: http://dx.doi.org/10.5772/intechopen.92076*

*Lessons Learned and Recent Advances in Dengue Research DOI: http://dx.doi.org/10.5772/intechopen.92076*

*Dengue Fever in a One Health Perspective*

reported in America, Africa, Mid-west, Asia and the Pacific islands [2]. Nearly 3 billion people (40% of world population) are at risk in areas where dengue occurs, and about 70% of the population at risk are in South East Asia and Western Pacific region [2]. About 400 million people are infected with dengue annually, of which 100 million people are sick and 22,000 die of severe dengue [3]. A virus, a vector and a sensitive population must be in the same geographic area for a dengue onset outbreak [1]. Travelers contribute to dengue dissemination to non-endemic areas but they may also serve as sentinels for warning dissemination. Some studies indicate that dengue represents about 2% of the diseases from travelers returning to from endemic areas [4]. Based on GeoSentinel, a data-collection network between 1997 and 2006, dengue was imported from South-east Asia (51%), South Central Asia (17%), Latin America (15%), the Caribbean (9%), parts of Africa (5%) and Oceania (2%) [4]. The number of febrile travelers returning from the tropics and sub-tropical areas being diagnosed with dengue has increased from 2% in the 1990s to 16% by 2005 [4]. A study of paedriatic travelers in 19 countries reported dengue and typhoid fever as the most often febrile diseases in children returning from tropical regions and sub-Saharan Africa [4]. *Aedes aegypti* vector can be disseminated relatively easy in urban areas because of its strong anthropophilic habits, its biological features like egg resistance to desiccation, its permanence within and not away from the urban centers, and the search for water with low load of organic matter for its oviposition making its arrival in rural areas, where the temperature enables its replication, relatively simple; transform cemeteries, tire repair shop, bus terminals, etc. in critical points of infestation where the vector surveillance must be carried out [5]. The virus can reach new areas where cases of symptomatic and asymptomatic persons or cases of people's incubation period of the disease have not been reported. Around three-quarters of dengue infections presented each year are clinically inapparent, the asymptomatic ones were considered dead-end hosts because they do not produce high enough viremia to infect mosquitoes [6]. Some studies provide evidence that despite a low level of viremia, dengue asymptomatic persons were capable of transmitting the disease to mosquitoes and potentially enabling a high virus transmission. Since it has no symptoms, they could continue in their day-to-day work and be exposed to mosquito bites [6]. The virus can also be spread through infected mosquitoes so that once the mosquito is infected and the extrinsic incubation period is passed, it can be a lifelong carrier of the virus which is about 2 weeks or a month. The interruption of dengue transmission was possible in the 60s and at the beginning of the 70s as a result of an *Aedes aegypti* eradication. The lack of surveillance and vector control followed outbreaks in the Caribbean, Central America and South America [1]. From this experience, it is considered that vector control and epidemiological services detecting and studying dengue cases have to work together and maintain a constant vigilance [1]. The monitoring service should be capable of making the difference between a seasonal and/or temporary increase and increases in the number of cases resulting from a dengue outbreak so that tools of epidemiology as the endemic channel are highly important. If the number of cases reported is higher in two standard deviations above the endemic channel in monthly or weekly notifications, a warning of dengue is produced [1, 7]. However, the lack of notifications continues to be one of the most significant problems in order to prevent and control this disease in many countries as well as in the western Pacific region [1]. The Geographic Information Systems (GIS) allows the analysis of this information on the geographical reference basis in space and time. This type of systems is important for vector-borne disease surveillance and vector control strategy planning [8]. DENV can be transmitted to humans through the bite of female mosquitoes of the *Aedes aegypti*. Other dengue transmission mechanism

**18**

is the perinatal transmission and it occurs when a mother is infected near the childbirth so that the infection can be transmitted through microtransfusion when a placental abruption occurs or during delivery when the mother's blood gets in contact with the newborn's mucosal. Dengue in pregnancy is related to premature delivery, fetal distress in labour, intrauterine death and miscarriages. DENV can also be transmitted through breast milk or exposure to blood, organs or infected tissues like bone marrow [9]. In a study carried out at the Brazilian blood center from February to June in 2012, donors tested positive for DENV-3 and DENV-4 were found and 42 units of PCR tested positive were transfused in 35 recipients. Of these findings, 16 units testing positive were transfused in 16 sensitive recipients in which 5 possible cases transmitted by transfusion (TT) were found, 1 case was considered as a possible TT, and 10 of them were not transmitted. However, no significant differences were found between symptoms and mortality in cases and controls [10].

#### **3. Dengue virus serotypes and genotypes and its relation to clinical cases**

The evolution of molecular biology and phylogenetic analysis has enabled molecular epidemiology studies binding DENV-phylogenetic analysis which was found in different geographic areas within a certain period of time and clinical and epidemiological data in order to establish a relation to genotypes and lineages which are found with other circulating strains as well as to identify the origin and the transmission route, the severity of the disease, etc. There are four related DENV serotypes but antigenically different DENV-1, DENV-2, DENV-3, DENV-4 and each of them generates an immune response to the infection. The nucleotide sequences show 63–68% homology within the DENV group in comparison with 44% between DENV and Yellow Fever virus (YFV), and 51% between DENV and West Nile virus (WNV), and it shares a minor homology at 80% at a level of amino acids [11]. Previous studies based on partial (prM/E), partial or complete E gene; or complete genomic sequences recognized distinct DENV genotypes [12] (**Table 1**).

The genotypes may present different lineages or clades. The genetic changes in the virus are caused by mutations or the introduction of a new variant from other region, thus genotyping of strain virus is used to identify the epidemic outbreak source and spread [12]. Some dengue genotypes are related to a higher virulence. DENV-2 and DENV-3 Asian genotypes are associated with severe infections [1]. In South East Asia, dengue hemorrhagic fever (DHF) and/or dengue shock syndrome (DSS) outbreaks are caused by DENV-2 southeast Asian genotype strain, meanwhile epidemics caused by DENV-2 in Latin America presents solely dengue fever (DF) in most cases. The DENV-2 genotypes circulating in the United States seem to be less virulent. Because of the introduction of the South East Asian genotype virulent, the number of cases of DHF and DSS in America has increased [1, 11].

It is thought that an infection with DENV serotype provides lifelong immunity against the same serotype infection and short-term protection against infection by a 2 or 3 month-heterologous serotype [1, 11]. Some studies contradict the hypothesis that has been accepted until now. In 2010–2011 a study in DENV-2 American/Asian genotype outbreak was conducted in Iquitos, Peru. It was carried out 15 years after the first DENV-2 American genotype in that region. The results on the study showed that protection against homologous DENV-2 may be incomplete [13]. In another study carried out in Peru, it was found that the antibodies of a primary infection against DENV-1 neutralized more efficiently in American DENV-2 than in Asian DENV-2. It is believed that this cross-protective immunity is not so strong to inhibit viremia but it may contribute to reduce DENV-2 infection


#### **Table 1.**

*Dengue virus serotypes and genotypes and its geographical distribution.*

symptomatology [14]. In 2013 evidences of a new dengue serotype appearance (DENV-5) that was identified in serum samples collected in 2007 during an epidemic in Malaysia were documented. Initially, it was thought that DENV-4 cases will circulate between primates and *Aedes nivalis* mosquitoes in the woods at South East Asia. However, it was shown that this virus was genetically different to DENV-4 from the rainforest and it had certain similarities to DENV-2 when the virus was isolated and after sequencing the whole genome, *rhesus macaques* were infected with four dengue serotypes. Once recovered from the infection, the monkeys were inoculated with DENV-5 which produced different antibodies. Moreover, it was observed that the infection with DENV-5 virus titer was four times higher than other serotypes. On the basis of this, it was concluded that DENV-5 will be a new serotype. It is thought that this new serotype may mainly circulate in nonhuman primates (NHP). This new serotype has only been found in the Woods of Sarawak [15]. However, there is a possibility that this new serotype may spread to human population becoming a public health concern. Thus, phylogenetics and epidemiological surveillance studies are required.

**21**

*Lessons Learned and Recent Advances in Dengue Research*

**4. Factors that increase dengue severity, cases and co-infection** 

the areas where the disease is spread may be the same leading potentially to

Most of dengue infections are subclinical or asymptomatic. Dengue epidemics were presented in Cuba in 1981 and 1987, and most cases of dengue shock and hemorrhagic dengue were mainly found in white population than in afro-descendants [16]. In studies carried out in Brazil and El Salvador, it was found that the African descent was a protective factor in dengue hemorrhagic manifestations [16]. In a dengue outbreak in Santiago de Cuba in 1997, it was found that hemorrhagic dengue cases were reported more frequently in patients aged between 15 and 39 years old. Additionally, they found a history of asthma in a 16.5% of the cases [17]. The WHO estimates that, by 2030, the diabetes mellitus will have been the 7th leading cause of death. A study carried out for evaluating the influence of diabetes mellitus and its relation to clinical manifestations of dengue, indicated higher risks of dengue symptoms potentially fatal within patients developing diabetes mellitus [18]. Other risk factors such as sickle-cell disease, uremia, allergies, hypertension, chronic renal failure may enable disease severity [1]. Regarding age, the lower compensation capacity of capillary plasma extravasation in children increases dengue shock risk. It has been observed that serious dengue cases were continuously presented in primary infections from breastfeeding babies whose mothers were developing immunity to some dengue serotype. The non-neutralizing antibodies produced by cross reaction during a primary infection or passively obtained from a mother to newborns are adhered to epitopes of dengue virus infections facilitating the entry of cells to Fc-receptors. This may contribute to a person's viral load increase resulting in strong immune response that includes inflammatory mediators [19]. Cytosines may enable plasma extravasation. In secondary infections, memory T-cells caused by previous reactions to dengue activate, replicate, produce cytosines and die of apoptosis. This can be correlated with disease severity [16]. The patient's background is important when ruling out other causes of this disease, for instance, other flavivirus presence like YFV, Saint Louis encephalitis virus (SLEV), Zika virus (ZIKV), WNV. Alphavirus like Chikungunya (CHIKV), Mayaro virus (MAYV), Venezuelan Equine Encephalitis virus (VEE), Bunyavirus like Oropouche virus (OROV), group C virus, Guaroa virus (GROV), Influenza virus, arenavirus, filovirus as well as other microorganisms can cause the disease with symptoms with similar symptoms such as malaria, Leptospirosis, typhoid fever, rickettsia diseases, etc. [1]. Dengue infections with different serotypes as well as the sequence of these infected patients may influence on the severity of the disease. In a study carried out in Singapore, between 2005 and 2011, febrile adult patients found in DENV-1 cases that were associated with dengue hemorrhagic fever (adjusted RR = 1.74) and severe dengue (adjusted RR = 2.1) were assessed, while DENV-2 had a low risk of dengue hemorrhagic fever (adjusted RR = 0.5) [20]. A special attention should be given to the clinical features of this disease in order to learn differences that lead to the identification of microorganisms causing the disease. It was found that there were no elevated hematocrit or shock cases in CHIKV infection as compared to dengue cases with high hematocrit in 40–69% of cases and shock in 10–39% of cases when comparing the clinical data and laboratory features within dengue infections and chikungunya [21]. The arthralgias were more frequent in CHIKV in 70–100% of cases as compared to at least 10% of dengue cases. The Zika infections may present Oedema in limbs as compared to dengue and chikungunya which is low or nil. The presence of this type of differences does not exclude atypical complications and presentations of the disease, thus the laboratory diagnosis plays a crucial role [22]. DENV, ZIKV and CHIKV are transmitted by *Aedes aegypti* vector. Therefore,

*DOI: http://dx.doi.org/10.5772/intechopen.92076*

**classification**

*Dengue Fever in a One Health Perspective*

Southeast Asian/ American

**Genotype Geographical distribution**

DENV-1 I Southeast Asia, China, The Middle East

Australia V The Americas, West Africa and Asia

Sylvatic West Africa and Southeast Asia

II Continental Southeast Asia III Asia, East Africa, the Americas

IV Puerto Rico and Tahiti

III Thailand IV Malaysia

*Dengue virus serotypes and genotypes and its geographical distribution.*

DENV-3 I Southeast Asia, the Philippines and the South Pacific islands

DENV-4 I The Philippines, Thailand, Vietnam, Myanmar, Malaysia, Sri Lanka, India

Americas

DENV-2 Asian I Thailand, Malaysia, Cambodia, Myanmar, Vietnam and Australia

IV Countries of the Pacific Rim, the Western Pacific, islands and

Asian II China, Indonesia, The Philippines, Taiwan, Sri Lanka, India, Honduras and Mexico

Cosmopolitan East and West Africa, the Middle East, the Indian subcontinent,

II Southeast Asia (Indonesia, Malaysia, Singapore), China, islands

American Central and South America, the Caribbean and the Indian subcontinent and the Pacific Islands

Southeast Asia, Central and South America and the Caribbean

of the Western Pacific Ocean, Australia, the Caribbean and the

Indian and Pacific Ocean Islands, Australia, Mexico

II Thailand III (Sylvatic) Malaysia

**Dengue serotype**

symptomatology [14]. In 2013 evidences of a new dengue serotype appearance (DENV-5) that was identified in serum samples collected in 2007 during an epidemic in Malaysia were documented. Initially, it was thought that DENV-4 cases will circulate between primates and *Aedes nivalis* mosquitoes in the woods at South East Asia. However, it was shown that this virus was genetically different to DENV-4 from the rainforest and it had certain similarities to DENV-2 when the virus was isolated and after sequencing the whole genome, *rhesus macaques* were infected with four dengue serotypes. Once recovered from the infection, the monkeys were inoculated with DENV-5 which produced different antibodies. Moreover, it was observed that the infection with DENV-5 virus titer was four times higher than other serotypes. On the basis of this, it was concluded that DENV-5 will be a new serotype. It is thought that this new serotype may mainly circulate in nonhuman primates (NHP). This new serotype has only been found in the Woods of Sarawak [15]. However, there is a possibility that this new serotype may spread to human population becoming a public health concern. Thus, phylogenetics and

epidemiological surveillance studies are required.

**20**

**Table 1.**
