Dengue Fever – Caused by a Mosquito

Timor-Leste has reported a surge of dengue cases since late 2021, at unusually high levels compared to previous years. There were 1451 reported cases and 10 deaths (CFR 0.7%) in 2020 and 901 cases and 11 deaths (CFR 1.2%) in 2021. In January 2022 alone 1286 cases were reported, of which 790 (61.4%) were children under the age of 14 years, 142 were severe dengue cases and 20 fatalities were reported (case fatality ratio 1.6%).

Figure 1. Dengue cases reported in Timor-Leste, 1 January 2016 – 31 January 2022

Source: WHO Country Office in Timor-Leste, WHO Regional Office for South-East Asia

ABOUT Dengue
Dengue is a mosquito-borne viral infection that is common in warm, tropical climates. Infection is caused by any one of four closely related dengue viruses (called serotypes including DENV-1, DENV-2, DENV-3 and DENV-4) and these can lead to a wide spectrum of symptoms, including some which are extremely mild (unnoticeable) to those that may require medical intervention and hospitalization. In severe cases, fatalities can occur. There is no treatment for the infection itself but the symptoms that a patient experiences can be managed.

Dengue epidemics tend to have seasonal patterns, with transmission often peaking during and after rainy seasons. Dengue has distinct epidemiological patterns, associated with the four serotypes of the virus. These can co-circulate within a region, and indeed many countries are hyper-endemic for all four serotypes. Dengue has an alarming impact on both human health and the global and national economies. DENV is frequently transported from one place to another by infected travellers; when susceptible vectors are present in these new areas, there is the potential for local transmission to be established.

DISTRIBUTIONS
The number of dengue cases reported to WHO increased over 8 fold over the last two decades, from 505,430 cases in 2000, to over 2.4 million in 2010, and 5.2 million in 2019. Reported deaths between the year 2000 and 2015 increased from 960 to 4032, affecting mostly younger age group. The total number of cases seemingly decreased during years 2020 and 2021, as well as for reported deaths. However, the data is not yet complete and COVID-19 pandemic might have also hampered case reporting in several countries.

In 2020, dengue affected several countries, with reports of increases in the numbers of cases in Bangladesh, Brazil, Cook Islands, Ecuador, India, Indonesia, Maldives, Mauritania, Mayotte (Fr), Nepal, Singapore, Sri Lanka, Sudan, Thailand, Timor-Leste and Yemen. Dengue continues to affect Brazil, India, Vietnam, the Philippines, Cook Islands, Colombia, Fiji, Kenya, Paraguay, Peru and, Reunion islands, in 2021.

The COVID-19 pandemic is placing immense pressure on health care and management systems worldwide. WHO has emphasized the importance of sustaining efforts to prevent, detect and treat vector-borne diseases during this pandemic such as dengue and other arboviral diseases, as case numbers increase in several countries and place urban populations at highest risk for both diseases. The combined impact of the COVID-19 and dengue epidemics could have devastating consequences on the populations at risk.

CLINICAL PRESENTATION
Dengue is a self-limiting febrile illness with symptoms ranging from asymptomatic to severe. Symptoms of dengue may be observed around 4–10 days after the bite of an infected mosquito. Common symptoms are like that of the flu, with patients experiencing:

    – fever
    – headaches
    – pain behind the eyes
    – muscle and joint pain
    – nausea/vomiting
    – rash
    – fatigue

As the disease progresses, patients can also suffer from respiratory distress, bleeding from the nose and gums and have a rapid drop in blood pressure leading to shock. If left unmanaged, this can lead to death. Sound case management of dengue in hospitals has helped to reduce case fatality rates to less than 1% in most affected countries.

TREATMENT
There is no specific treatment for dengue fever. Patients should rest, stay hydrated and seek medical advice. Depending on the clinical manifestations and other circumstances, patients may be sent home, be referred for in-hospital management, or require emergency treatment and urgent referral.

DIAGNOSIS
Several methods can be used for diagnosis of DENV infection. Depending on the time of patient presentation, the application of different diagnostic methods may be more or less appropriate. Patient samples collected during the first week of illness should be tested by both methods mentioned below:
Virus isolation methods
The virus may be isolated from the blood during the first few days of infection. Various reverse transcriptase–polymerase chain reaction (RT–PCR) methods are available and are considered the gold standard. However, they require specialised equipment and training for staff to perform these tests.
The virus may also be detected by testing for a virus-produced protein, called NS1. Genesis provides commercially-produced rapid diagnostic tests for this, and it takes only ~10 mins to determine the result, and the test does not require specialized laboratory techniques or equipment.
Serological methods
Serological methods, such as enzyme-linked immunosorbent assays (ELISA), may confirm the presence of a recent or past infection, with the detection of anti-dengue antibodies. IgM antibodies are detectable ~1 week after infection and remain detectable for about 3 months. The presence of IgM is indicative of a recent DENV infection. IgG antibody levels take longer to develop and remains in the body for years. The presence of IgG is indicative of a past infection.

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