**1.3 Epidemiology of other metaxenic diseases**

The propagation of the vector for decades is conditioned by the climatic changes. For example, in May 2004, heat waves and droughts were observed in the coastal areas of Kenya, toward Lamu and Mombasa, two large coastal cities. That period was also the beginning of a large chikungunya outbreak in these two cities (with reported attack rates of 75%) before its spread to the Indian Ocean [14]. Entomologists have explained how and why droughts can be associated with increases in diseases transmitted by *Aedes*, such as chikungunya, dengue, Zika, and yellow fever [15, 16]. During droughts, due to water scarcity, people store a greater amount of water outside or inside the home for longer periods of time, providing shelters to mosquito eggs and larvae [13].

In Peru, the consequence of this weather phenomenon allowed the dissemination of the *Aedes* vector and consequently led to the increase in cases of emerging diseases, such as Zika and chikungunya (**Figure 2**). Thus, from 2016 to 2018, 1113 gestating women entered the surveillance system for Zika, of which 61% were notified in 2017. Of the total number of pregnant women notified, 31% had laboratory confirmation for Zika virus through molecular tests like polymerase chain reactionreverse transcription (RT-PCR) [7].

## **1.4 Dengue and coinfections**

The fluvial precipitations that the phenomenon of the coastal El Niño brought with it during 2017 triggered the collapse of the sewerage system, generating floods and the exposure of wastewater, which together with the rains gave an adequate

#### **Figure 2.**

*Distribution of indigenous cases of Zika by onset of symptoms. Peru 2016–2017. Taken from: Ministry of Health of Peru MINSA [17].*

environment for the transmission of leptospirosis in urban areas of the Lambayeque region. It was even possible to demonstrate that during this period, laboratory findings compatible with dengue and leptospirosis were reported simultaneously. While it is true that many of the immunoglobulin can remain for years in the patient and do not necessarily require an acute infection, the similarity of clinical symptoms between dengue and leptospirosis makes both pathologies confusing to health personnel, even more so during the appearance of a weather phenomenon where there is an outbreak [18].

#### **1.5 Dengue and seasonality**

Dengue in Ecuador fluctuates with a very similar seasonality. The season is an important determinant of infectious disease rates, including mosquito-propagated arboviruses, such as dengue, chikungunya, and Zika. Seasonal disease patterns are driven by a combination of climatic or environmental factors, such as temperature or rainfall, and trends in human behavior time, such as school year schedules, vacations, and weekend patterns. These factors affect both disease rates and medical careseeking behavior. The seasonality of dengue fever has been studied in the context of climatic factors. Thus, between 2009 and 2016, a predictive model of dengue detection was studied using data from the same patients in rural areas in Ecuador. Thus, compared to the average of every day, cases were more likely to be diagnosed on Tuesdays (relative risk [RR]: 1.26; 95% confidence interval [CI]: 1.05–1.51) and Thursdays (RR: 1.25; 95% CI: 1.02–1.53), and were less likely to be diagnosed on Saturdays (RR: 0.81; 95% CI: 0.65–1.01) and Sundays (RR: 0.74; 95% CI: 0.58–0.95). The holidays were not significant predictors of dengue diagnoses, except for an increase in diagnoses the day after Christmas (RR: 2.77; 95% CI: 1.46–5.24) [19].

From the political sphere, the coastal El Niño phenomenon caused the Ministry of Health and the Ministry of Defense of Ecuador to take into account the declaration of emergency for the Peruvian city of Piura, issued by the Ministry of Health of that country. This is because that city is close to the border of Ecuador, and the trade between the two countries is very high, which makes it necessary to work in a multisectoral way to eradicate the vector [20].

#### **1.6 Impact on the epidemiological surveillance system**

It is very necessary to maintain entomological surveillance, especially in those cities where the phenomenon left vector presence. Migration and population increase, in addition to raising awareness and educating the population about the risk factors of dengue occurrence, should always be taken into account to avoid a disease that was installed in the Americas decades ago, precisely because of migration from other areas. The consequences of climate change must be learned as it not only destroys our habitat but directly interferes with our health [21]. Health authorities have the responsibility to plan strategies and evaluate their impact progressively. Many times it is not enough to plan, but to change strategies to avoid having the same results.

### **2. Clinical behavior of dengue**

#### **2.1 Definitions**

Classically, the disease presents with an incubation period of 3–14 days; after that a febrile phase (1–4 days); viremia, the critical phase from 4 to 7 days; and a

**37**

**Figure 3.**

*et al. [29].*

*Situation of Dengue after the Phenomenon of the Coastal El Niño*

arthralgia, low back pain, rash, and nausea [23, 24].

status, increased hematocrit, and hepatomegaly [23, 24].

involvement (encephalitis, hepatitis, and myocarditis) [25].

recovery phase from day 7 onward [22]. This disease course depends on the virus serotype and whether or not the individual has previously had a dengue infection.

• Dengue without warning signs: Person with a fever of 7 or less days, with at least two of the following symptoms such as eye pain, myalgia, headache,

• Dengue with warning signs: Person with a probable case of dengue with one or more of the clinical signs such as severe abdominal pain, dyspnea, serous effusion, persistent vomiting, hypothermia, mucosal bleeding, altered mental

• Severe dengue: A probable case with or without warning signs presenting one of the following signs such as signs of hypovolemic shock, severe bleeding, respiratory distress syndrome due to plasma extravasation, and severe organ

It is known that the cross-immunity of dengue serotypes is limited, which increases

the possibility of reinfections and with them more florid clinical pictures [25, 26]. Previous studies observed the outbreaks from 2010 onward, observing that dengue cases occurred in a greater proportion due to DENV-2, the most frequent clinical symptom being retro-ocular pain, myalgias associated with a 7-day fever [27]. Also, it was observed that in dengue cases, many of them were reinfections and DENV-2 continued to prevail, which was one of the worst at presenting cross-

A study conducted in the north coast of Peru found that, among the referred symptoms, 82% reported fever, being less than half quantified (values from 37to 41°C), followed by headache (75.6%), arthralgias (69.7%), myalgias (62.4%), retroocular pain (55.5%), lumbar pain (44.7%), and only 24.4% presenting rash. The presence of platelet decrease (78.4%) was the most frequent among cases with

*Age distribution of DENV-neutralizing antibodies in 2010. Samples were collected between March and June 2010, approximately 6 months prior to a large dengue epidemic largely caused by American/Asian genotype DENV-2. Panel A: Age distribution of serotype-specific DENV-neutralizing antibodies. Panel B: Age distribution of number of prior DENV infections. Naive indicates absence of detectable DENV-neutralizing antibodies against any serotype, monotypic indicates DENV-neutralizing antibodies against one serotype, and multitypic indicates DENV-neutralizing antibodies against two or more serotypes. Taken from: Forshey* 

*DOI: http://dx.doi.org/10.5772/intechopen.92095*

In this spectrum of disease, one can have:

**2.2 Signs and symptoms**

immunity (**Figure 3**).

alarm signs [28] (**Figure 4**).

recovery phase from day 7 onward [22]. This disease course depends on the virus serotype and whether or not the individual has previously had a dengue infection. In this spectrum of disease, one can have:


### **2.2 Signs and symptoms**

*Dengue Fever in a One Health Perspective*

there is an outbreak [18].

**1.5 Dengue and seasonality**

multisectoral way to eradicate the vector [20].

**1.6 Impact on the epidemiological surveillance system**

environment for the transmission of leptospirosis in urban areas of the Lambayeque region. It was even possible to demonstrate that during this period, laboratory findings compatible with dengue and leptospirosis were reported simultaneously. While it is true that many of the immunoglobulin can remain for years in the patient and do not necessarily require an acute infection, the similarity of clinical symptoms between dengue and leptospirosis makes both pathologies confusing to health personnel, even more so during the appearance of a weather phenomenon where

Dengue in Ecuador fluctuates with a very similar seasonality. The season is an important determinant of infectious disease rates, including mosquito-propagated arboviruses, such as dengue, chikungunya, and Zika. Seasonal disease patterns are driven by a combination of climatic or environmental factors, such as temperature or rainfall, and trends in human behavior time, such as school year schedules, vacations, and weekend patterns. These factors affect both disease rates and medical careseeking behavior. The seasonality of dengue fever has been studied in the context of climatic factors. Thus, between 2009 and 2016, a predictive model of dengue detection was studied using data from the same patients in rural areas in Ecuador. Thus, compared to the average of every day, cases were more likely to be diagnosed on Tuesdays (relative risk [RR]: 1.26; 95% confidence interval [CI]: 1.05–1.51) and Thursdays (RR: 1.25; 95% CI: 1.02–1.53), and were less likely to be diagnosed on Saturdays (RR: 0.81; 95% CI: 0.65–1.01) and Sundays (RR: 0.74; 95% CI: 0.58–0.95). The holidays were not significant predictors of dengue diagnoses, except for an increase in diagnoses the day after Christmas (RR: 2.77; 95% CI: 1.46–5.24) [19].

From the political sphere, the coastal El Niño phenomenon caused the Ministry of Health and the Ministry of Defense of Ecuador to take into account the declaration of emergency for the Peruvian city of Piura, issued by the Ministry of Health of that country. This is because that city is close to the border of Ecuador, and the trade between the two countries is very high, which makes it necessary to work in a

It is very necessary to maintain entomological surveillance, especially in those

Classically, the disease presents with an incubation period of 3–14 days; after that a febrile phase (1–4 days); viremia, the critical phase from 4 to 7 days; and a

cities where the phenomenon left vector presence. Migration and population increase, in addition to raising awareness and educating the population about the risk factors of dengue occurrence, should always be taken into account to avoid a disease that was installed in the Americas decades ago, precisely because of migration from other areas. The consequences of climate change must be learned as it not only destroys our habitat but directly interferes with our health [21]. Health authorities have the responsibility to plan strategies and evaluate their impact progressively. Many times it is not enough to plan, but to change strategies to avoid

**36**

having the same results.

**2.1 Definitions**

**2. Clinical behavior of dengue**

It is known that the cross-immunity of dengue serotypes is limited, which increases the possibility of reinfections and with them more florid clinical pictures [25, 26].

Previous studies observed the outbreaks from 2010 onward, observing that dengue cases occurred in a greater proportion due to DENV-2, the most frequent clinical symptom being retro-ocular pain, myalgias associated with a 7-day fever [27]. Also, it was observed that in dengue cases, many of them were reinfections and DENV-2 continued to prevail, which was one of the worst at presenting crossimmunity (**Figure 3**).

A study conducted in the north coast of Peru found that, among the referred symptoms, 82% reported fever, being less than half quantified (values from 37to 41°C), followed by headache (75.6%), arthralgias (69.7%), myalgias (62.4%), retroocular pain (55.5%), lumbar pain (44.7%), and only 24.4% presenting rash. The presence of platelet decrease (78.4%) was the most frequent among cases with alarm signs [28] (**Figure 4**).

#### **Figure 3.**

*Age distribution of DENV-neutralizing antibodies in 2010. Samples were collected between March and June 2010, approximately 6 months prior to a large dengue epidemic largely caused by American/Asian genotype DENV-2. Panel A: Age distribution of serotype-specific DENV-neutralizing antibodies. Panel B: Age distribution of number of prior DENV infections. Naive indicates absence of detectable DENV-neutralizing antibodies against any serotype, monotypic indicates DENV-neutralizing antibodies against one serotype, and multitypic indicates DENV-neutralizing antibodies against two or more serotypes. Taken from: Forshey et al. [29].*

#### **Figure 4.**

*Symptomatology of patients diagnosed with dengue. (A) Symptoms and signs. (B) Warning signs. Taken from: Perales-Carrasco et al. [28].*

#### **2.3 Signs and symptoms in coinfections**

In recent years, new viruses such as chikungunya (CHIKV) and Zika (ZIKV) have also been introduced. In recent years after the ZIKV epidemic, cases of ZIKV infection have continued to be observed, and in children, according to Salgado et al. [30], there were found patients with encephalitis with coinfection of DENV and ZIKV.

Another study, also conducted in Peru, showed that the circulating serotypes during the coastal El Niño phenomenon were DENV-2 and DENV-3, as well as confirmed cases of CHIKV and ZIKV, even in high Andean areas; concomitantly, the study revealed that the main symptoms of dengue were headaches, arthralgias, and back pain associated with fever (**Table 1**) [27].

Taken from: Forshey et al. [29].

In Peru, there could be a subdiagnosis or overdiagnosis of dengue and therefore of the clinical variability, on the one hand; the amount of arbovirosis that can give a similar clinical presentation is wide, and within these viruses is oropuche, which can be confused with dengue during the endemic months [31]. The contrary occurs in patients with a second dengue virus infection in which the diagnostic methods have a lower sensitivity of 60%, as is the case of non-structural (NS1), a test widely used in our environment [26].

The Huánuco region, located in the center of Peru, was one of the cities that presented an increase in dengue cases, where about 90% of patients presented with myalgia, headache, and rash; being in these patients a diagnostic confirmation of 92% by PCR. This being an area with low endemicity, but as a result of coastal El Niño, it could mean a majority of primary infection, and therefore this high rate of clinical diagnostic correlation [26]. In addition, it is important to know the behavior in children under 5 years of age, in which many of them have antigens from mothers in endemic areas, which leads to more severe manifestations being possible in this particular age group [32].

Finally, it can be observed that, in the years before the dengue virus infection, the agent (DENV-2) and the clinical manifestations were similar, with the difference in the number of cases and the increase in coinfections of the new circulating

**39**

**Table 1.**

*Situation of Dengue after the Phenomenon of the Coastal El Niño*

**Clinical symptoms Total n = 496 (%) PCR real-time confirmed cases**

**DENV (n = 170)**

Chills 3 (0.6) 1 (0.6) 0 (0.0) 0 (0.0) Headache 444 (89.5) 152 (89.4) 34 (87.2) 20 (87.0) Dizziness 1 (0.2) 0 (0.0) 1 (2.6) 0 (0.0) Cough 1 (0.2) 1 (0.6) 0 (0.0) 0 (0.0) Sore throat 184 (37.1) 50 (29.4) 11 (28.2) 11 (47.8) Nausea and/or vomits 251 (50.6) 86 (50.6) 20 (51.3) 13 (56.5) Loss of appetite 312 (62.9) 104 (61.2) 23 (59.0) 18 (78.3) Back pain 270 (54.4) 105 (61.8) 23 (59.0) 17 (73.9) Dysuria 1 (0.2) 0 (0.0) 0 (0.0) 0 (0.0) Myalgia 419 (84.5) 147 (86.5) 35 (89.7) 17 (73.9) Arthralgia 396 (79.8) 143 (84.1) 32 (82.1) 19 (82.6) Retro-ocular pain 337 (67.9) 118 (69.4) 27 (69.2) 17 (73.9) Rash 89 (17.9) 26 (15.3) 8 (20.5) 6 (26.1) Melena 2 (0.4) 0 (0.0) 0 (0.0) 0 (0.0) Nasal bleeding 9 (1.8) 3 (1.8) 1 (2.6) 1 (4.3) Gums bleeding 3 (0.6) 2 (1.2) 1 (2.6) 0 (0.0) Petechiae 11 (2.2) 3 (1.8) 0 (0.0) 1 (4.3) Ecchymosis 2 (0.4) 1 (0.6) 1 (2.6) 0 (0.0) Blood-tinged sputum 1 (0.2) 0 (0.0) 0 (0.0) 0 (0.0) Abdominal pain 22 (4.4) 7 (4.1) 1 (2.6) 1 (4.3) Thoracic pain 5 (1.0) 2 (1.2) 0 (0.0) 0 (0.0) Fatigue 3 (0.6) 0 (0.0) 1 (2.6) 0 (0.0) Altered mental status 1 (0.2) 1 (0.6) 0 (0.0) 1 (4.3)

**ZIKV (n = 39)**

**n (%) n (%) n (%)**

**CHIKV (n = 23)**

viruses; this should make the health staff reflect on making proper use of diagnostic tests to provide better care and avoid fatal outcomes, as it was in some cases dis-

Today, there are guidelines established by international organizations for the rational use of dengue diagnostic tests. The World Health Organization (WHO) recommends the use of polymerase chain reaction (PCR) for the early detection of dengue and its complementation with other tests such as immunoglobulin M (IgM), immunoglobulin G (IgG), and NS1 [33]; however, the use according to the clinical picture and the time of the disease will favor the optimal use of the different tests. The sensitivity and specificity of the NS1 antigen test can range from 49 to 59% and from 93 to 99%, respectively, while that of the IgM antibody test is from 71 to

cussed above in the last phenomenon of the coastal El Niño (**Table 2**).

*Clinical symptoms in patients with positive samples for DENV, ZIKV, and CHIKV.*

**3. Laboratory in the diagnosis of dengue**

*DOI: http://dx.doi.org/10.5772/intechopen.92095*


*Situation of Dengue after the Phenomenon of the Coastal El Niño DOI: http://dx.doi.org/10.5772/intechopen.92095*

#### **Table 1.**

*Dengue Fever in a One Health Perspective*

**2.3 Signs and symptoms in coinfections**

**Figure 4.**

*Perales-Carrasco et al. [28].*

and back pain associated with fever (**Table 1**) [27].

Taken from: Forshey et al. [29].

used in our environment [26].

particular age group [32].

In recent years, new viruses such as chikungunya (CHIKV) and Zika (ZIKV) have also been introduced. In recent years after the ZIKV epidemic, cases of ZIKV infection have continued to be observed, and in children, according to Salgado et al. [30], there

*Symptomatology of patients diagnosed with dengue. (A) Symptoms and signs. (B) Warning signs. Taken from:* 

Another study, also conducted in Peru, showed that the circulating serotypes during the coastal El Niño phenomenon were DENV-2 and DENV-3, as well as confirmed cases of CHIKV and ZIKV, even in high Andean areas; concomitantly, the study revealed that the main symptoms of dengue were headaches, arthralgias,

In Peru, there could be a subdiagnosis or overdiagnosis of dengue and therefore of the clinical variability, on the one hand; the amount of arbovirosis that can give a similar clinical presentation is wide, and within these viruses is oropuche, which can be confused with dengue during the endemic months [31]. The contrary occurs in patients with a second dengue virus infection in which the diagnostic methods have a lower sensitivity of 60%, as is the case of non-structural (NS1), a test widely

The Huánuco region, located in the center of Peru, was one of the cities that presented an increase in dengue cases, where about 90% of patients presented with myalgia, headache, and rash; being in these patients a diagnostic confirmation of 92% by PCR. This being an area with low endemicity, but as a result of coastal El Niño, it could mean a majority of primary infection, and therefore this high rate of clinical diagnostic correlation [26]. In addition, it is important to know the behavior in children under 5 years of age, in which many of them have antigens from mothers in endemic areas, which leads to more severe manifestations being possible in this

Finally, it can be observed that, in the years before the dengue virus infection, the agent (DENV-2) and the clinical manifestations were similar, with the difference in the number of cases and the increase in coinfections of the new circulating

were found patients with encephalitis with coinfection of DENV and ZIKV.

**38**

*Clinical symptoms in patients with positive samples for DENV, ZIKV, and CHIKV.*

viruses; this should make the health staff reflect on making proper use of diagnostic tests to provide better care and avoid fatal outcomes, as it was in some cases discussed above in the last phenomenon of the coastal El Niño (**Table 2**).

### **3. Laboratory in the diagnosis of dengue**

Today, there are guidelines established by international organizations for the rational use of dengue diagnostic tests. The World Health Organization (WHO) recommends the use of polymerase chain reaction (PCR) for the early detection of dengue and its complementation with other tests such as immunoglobulin M (IgM), immunoglobulin G (IgG), and NS1 [33]; however, the use according to the clinical picture and the time of the disease will favor the optimal use of the different tests.

The sensitivity and specificity of the NS1 antigen test can range from 49 to 59% and from 93 to 99%, respectively, while that of the IgM antibody test is from 71 to


*Note: N.E.: Not estimable. Taken from: Paternina-Caicedo et al. [32].*

*\*Adjusted by age, days with symptoms, and sex.*

*\*\*Fisher's exact test.*

*\*\*\*Best fit was the natural logarithm of the exposure variable.*

#### **Table 2.**

*Clinical and laboratory characteristics of chikungunya and dengue and their relative adjusted risks among children <24 months of age in Colombia.*

80% and 46 to 90%, respectively, considering a median of 5 days of fever before the collection of the samples (interquartile range of 3–7 days) for the two tests mentioned. The diagnostic accuracy for the detection of IgM increases for late acute infection (5 days after the onset of symptoms) compared to the early one. The NS1 antigen is an early marker of acute infection, and its combined use with IgM detection can provide a definitive diagnosis of 96.9–100% for samples obtained after 3 days of illness [33]. The reported sensitivity and specificity of IgG for dengue are 92.0 and 100%, respectively [34].

The patient usually has an incubation period of 4–5 days after the bite by mosquitoes of the *Aedes* genus, then presents a clinical picture with variable signs and symptoms for a period of 4–5 days, a period in which he presents the virus of the dengue circulating in the bloodstream and can transmit the disease to other patients through new bites by the aforementioned vector, so techniques based on virus isolation, through cultures, or the detection of genomic material, such as PCR, require samples taken during this time. The end of the patient's clinical picture is usually manifested by a generalized maculopapular rash, which indicates recovery and can guide the use of serological tests, such as the detection of IgM and IgM antibodies, since the viral load values in the patient have disappeared or significantly reduced, which would make the use of molecular tests or culture inefficient. Leukopenia can be found at this stage with normal platelet and transaminase counts [3].

**41**

**Figure 5.**

*Almanzor Aguinaga Asenjo, Hospital, Essalud.*

serology [38].

*Situation of Dengue after the Phenomenon of the Coastal El Niño*

We can summarize the diagnostic tests used for dengue in four groups: (i) virus isolation and characterization, (ii) detection of the genomic sequence through a nucleic acid amplification test, (iii) detection of specific antibodies against the virus, and (iv) identification of dengue virus (glycoprotein) antigens. Isolation of the virus is achieved by cell culture that gives the most specific result, and the sera are usually collected in the first 3–5 days after the fever starts. Virus isolation is highly dependent on viral load, which limits the period during which the virus can be successfully isolated in the patient's serum. In addition, its high cost makes this test little accessible to most laboratories [3]. Viral identification can also be done using dengue-specific monoclonal antibodies by immunofluorescence and reverse

On the other hand, serological tests are relatively inexpensive and easy to perform. These characteristics make them the most used tests for dengue infection. IgM levels begin to rise on the third day of a primary infection and peak at 2 weeks after the onset of fever (**Figure 5**). IgG is detectable at the end of the first week of illness and may persist for life. Enzyme-linked immunosorbent assay (ELISA) tests can analyze the levels of IgM and IgG, and the IgM/IgG ratio is useful to distinguish primary from secondary infections. The IgM/IgG ratio greater than 1.4 is indicative of primary dengue infection, while the IgM/IgG ratio lesser than 1.2 is indicative of secondary dengue infection. The potential cross-reactivity of dengue virus with other flaviviridae when using serological assays remains a significant limitation for its use. Prior vaccination against yellow fever can also lead to a false positive serological test for dengue virus. The prolonged period of seroconversion also results in false negatives [3]. All flaviviruses produce a glycoprotein called NS1 and tests such as antigen capture ELISA and quick tests based on immunochromatography can be used to identify it in the bloodstream; it is detectable from days 0 to 9 after the onset of symptoms, although detection appears to be higher in the samples collected up to 3 days after the onset of symptoms. Quick tests are now available and provide results in 15 min. Rapid tests for NS1 have been estimated to have a significantly higher sensitivity for primary infections (94.7%) than for secondary infections (67.1%; p < 0.001) and now appear to be a potential alternative to culture, PCR, and

The Brazilian Ministry of Health recommends that samples of patients with suspected dengue fever taken up to 8 days (preferably 5) after the onset of symptoms should be processed using ELISA for the detection of NS1 and qRT PCR for the detection of the DENV genome and the serotype. At 8–15 days after the onset of symptoms, the samples are analyzed for IgM detection using ELISA. After 15 days,

*(A) Primary infection by dengue. (B) Secondary infection by dengue. Source: Clinical Pathology Department,* 

*DOI: http://dx.doi.org/10.5772/intechopen.92095*

transcription-PCR (RT-PCR) [3].

*Situation of Dengue after the Phenomenon of the Coastal El Niño DOI: http://dx.doi.org/10.5772/intechopen.92095*

*Dengue Fever in a One Health Perspective*

Clinical

Laboratory

(IQR) [n]

cells/ml) Median (IQR) [n]

*\*\*Fisher's exact test.*

**Table 2.**

Hemoglobin (mg/dl) median (interquartile range (IQR)) [n]

Hematocrit (%) median

White blood cells (1000

*Note: N.E.: Not estimable. Taken from: Paternina-Caicedo et al. [32].*

*\*\*\*Best fit was the natural logarithm of the exposure variable.*

80% and 46 to 90%, respectively, considering a median of 5 days of fever before the collection of the samples (interquartile range of 3–7 days) for the two tests mentioned. The diagnostic accuracy for the detection of IgM increases for late acute infection (5 days after the onset of symptoms) compared to the early one. The NS1 antigen is an early marker of acute infection, and its combined use with IgM detection can provide a definitive diagnosis of 96.9–100% for samples obtained after 3 days of illness [33]. The reported sensitivity and specificity of IgG for dengue are

*Clinical and laboratory characteristics of chikungunya and dengue and their relative adjusted risks among* 

**Characteristics Crude analysis Risks for dengue**

Diarrhea, n (%) 3/37 (8) 13/57 (23) 0.064 2.13 (0.29–15.66) Ascites, n (%) 0/37 (0) 1/57 (2) 1.000\*\* N.E. Pleural effusion, n (%) 0/37 (0) 2/56 (4) 0.516 N.E.

10.5 (10–12) [35] 10.5 (10–12)

Decrease for age, n (%) 26/36 (72) 25/53 (47) 0.019 1.33 (0.26–6.87) Increase for age, n (%) 0/36 (0) 1/53 (2) 1.000\*\* N.E.

30.9 (29–34) [33] 31.5 (30–35)

Decrease for age, n (%) 24/33 (73) 30/52 (58) 0.160 1.04 (0.26–4.19) Increase for age, n (%) 0/33 (0) 1/52 (2) 1.000\*\* N.E.

6.4 (5–10) [33] 7.4 (5–12)

Decrease for age, n (%) 17/33 (52) 16/53 (30) 0.048 0.28 (0.07–1.08) Increase for age, n (%) 4/33 (12) 5/53 (9) 0.728 1.97 (0.27–14.17)

[36]

[37]

[36]

**Chikungunya Dengue p-value Adjusted odds ratio** 

0.910

a. 0.510

0.220

**(95% CI)\***

The patient usually has an incubation period of 4–5 days after the bite by mosquitoes of the *Aedes* genus, then presents a clinical picture with variable signs and symptoms for a period of 4–5 days, a period in which he presents the virus of the dengue circulating in the bloodstream and can transmit the disease to other patients through new bites by the aforementioned vector, so techniques based on virus isolation, through cultures, or the detection of genomic material, such as PCR, require samples taken during this time. The end of the patient's clinical picture is usually manifested by a generalized maculopapular rash, which indicates recovery and can guide the use of serological tests, such as the detection of IgM and IgM antibodies, since the viral load values in the patient have disappeared or significantly reduced, which would make the use of molecular tests or culture inefficient. Leukopenia can

be found at this stage with normal platelet and transaminase counts [3].

**40**

92.0 and 100%, respectively [34].

*\*Adjusted by age, days with symptoms, and sex.*

*children <24 months of age in Colombia.*

We can summarize the diagnostic tests used for dengue in four groups: (i) virus isolation and characterization, (ii) detection of the genomic sequence through a nucleic acid amplification test, (iii) detection of specific antibodies against the virus, and (iv) identification of dengue virus (glycoprotein) antigens. Isolation of the virus is achieved by cell culture that gives the most specific result, and the sera are usually collected in the first 3–5 days after the fever starts. Virus isolation is highly dependent on viral load, which limits the period during which the virus can be successfully isolated in the patient's serum. In addition, its high cost makes this test little accessible to most laboratories [3]. Viral identification can also be done using dengue-specific monoclonal antibodies by immunofluorescence and reverse transcription-PCR (RT-PCR) [3].

On the other hand, serological tests are relatively inexpensive and easy to perform. These characteristics make them the most used tests for dengue infection. IgM levels begin to rise on the third day of a primary infection and peak at 2 weeks after the onset of fever (**Figure 5**). IgG is detectable at the end of the first week of illness and may persist for life. Enzyme-linked immunosorbent assay (ELISA) tests can analyze the levels of IgM and IgG, and the IgM/IgG ratio is useful to distinguish primary from secondary infections. The IgM/IgG ratio greater than 1.4 is indicative of primary dengue infection, while the IgM/IgG ratio lesser than 1.2 is indicative of secondary dengue infection. The potential cross-reactivity of dengue virus with other flaviviridae when using serological assays remains a significant limitation for its use. Prior vaccination against yellow fever can also lead to a false positive serological test for dengue virus. The prolonged period of seroconversion also results in false negatives [3]. All flaviviruses produce a glycoprotein called NS1 and tests such as antigen capture ELISA and quick tests based on immunochromatography can be used to identify it in the bloodstream; it is detectable from days 0 to 9 after the onset of symptoms, although detection appears to be higher in the samples collected up to 3 days after the onset of symptoms. Quick tests are now available and provide results in 15 min. Rapid tests for NS1 have been estimated to have a significantly higher sensitivity for primary infections (94.7%) than for secondary infections (67.1%; p < 0.001) and now appear to be a potential alternative to culture, PCR, and serology [38].

The Brazilian Ministry of Health recommends that samples of patients with suspected dengue fever taken up to 8 days (preferably 5) after the onset of symptoms should be processed using ELISA for the detection of NS1 and qRT PCR for the detection of the DENV genome and the serotype. At 8–15 days after the onset of symptoms, the samples are analyzed for IgM detection using ELISA. After 15 days,

#### **Figure 5.**

*(A) Primary infection by dengue. (B) Secondary infection by dengue. Source: Clinical Pathology Department, Almanzor Aguinaga Asenjo, Hospital, Essalud.*

the sera are selected for IgG using ELISA. Dengue infection cannot be excluded in samples that are negative for the NS1 antigen and must be confirmed by IgM/IgG detection [35].

Cases of DENV-2 had a higher proportion of severe dengue than among those of DENV-1 and DENV-4 [39]. Nevertheless, the secondary infection was not a predictor of severe clinical manifestation in adults, who were primarily infected with serotype DENV-3 [40]; on the other hand, the dengue in children have suggested that infection with secondary DENV-2 is more likely to result in severe disease compared with other serotypes [41].

The fifth variant DENV-5 has been isolated in October 2013. This serotype follows the sylvatic cycle unlike the other four serotypes which follow the human cycle. The likely cause of emergence of the new serotype could be genetic recombination, natural selection, and genetic bottlenecks [42].
