DENGUE- AN OVERVIEW ON EMERGING EPIDEMIC IN INDIA.

Dengue, a mosquito-borne disease, has over the last few years become a major public health concern globally. There is more than thirty fold increase in number of cases worldwide in last five decades.

In India, 31,464 dengue cases and 36 related deaths reported between January and July 31, 2023 according to data published by National Centre for Vector Borne Disease Control Program. Most cases are detected in Kerela, Karnataka and Maharashtra.

Dengue is a vector-borne disease that is a major public health threat globally. It is caused by the dengue virus (DENV, 1–5 serotypes), which is one of the most important arboviruses in tropical and subtropical regions. Both Aedes aegypti and Aedes albopictus are the main competent vectors for dengue virus in India.

The epidemiology of dengue in India was first reported in Chennai in 1780, and the first outbreak occurred in Kolkata in 1963; subsequent outbreaks have been reported in different parts of India.

The expansion of dengue in India has been related to unplanned urbanization, changes in environmental factors, host–pathogen interactions and population immunological factors. Inadequate vector control measures have also created favourable conditions for dengue virus transmission and its mosquito vectors.

Recent studies have shown that seasonal mean temperature in India has increased significantly over the past with increase in the dengue risk by increasing the mosquito development rate and shortening the virus incubation time, thereby increasing the rate of transmission.

The commonest vector, Aedes aegypti is a small, dark coloured mosquito that has white lyre-shaped markings and banded legs. The mosquito usually bites people indoors and lays eggs during the daytime in water that contains organic material like leaves, algae etc. After feeding on a DENV-infected person, the virus replicates in the mosquito midgut before disseminating to secondary tissues, including the salivary glands. The time it takes from ingesting the virus to actual transmission to a new host is termed the extrinsic incubation period (EIP). The EIP takes about 8–12 days when the ambient temperature is between 25–28°C. Variations in the extrinsic incubation period are not only influenced by ambient temperature; several factors such as the magnitude of daily temperature fluctuations, virus genotype, and initial viral concentration can also alter the time it takes for a mosquito to transmit the virus. Once infectious, the mosquito can transmit the virus for the rest of its life. Human-to-mosquito transmission can occur up to 2 days before someone shows symptoms of the illness, and up to 2 days after the fever has resolved.

The risk of mosquito infection is positively associated with high viremia and high fever in the patient; conversely, high levels of DENV-specific antibodies are associated with a decreased risk of mosquito infection. Most people are viremic for about 4–5 days, but viremia can last as long as 12 days. The primary mode of transmission of DENV between humans involves mosquito vectors. There is evidence however, of the possibility of maternal transmission . At the same time, vertical transmission rates appear low, with the risk of vertical transmission seemingly linked to the timing of the dengue infection during the pregnancy. When a mother does have a DENV infection when she is pregnant, babies may suffer from pre-term birth, low birthweight, and fetal distress.

Rare cases of transmission via blood products, organ donation and transfusions have been recorded. Similarly, transovarial transmission of the virus within mosquitoes have also been recorded.

The clinical presentations of dengue viral infections range from asymptomatic to severe illness that may lead to death if not properly managed. The symptomatic cases are categorized as undifferentiated febrile illness (UF), dengue fever (DF), dengue haemorrhagic fever (DHF), dengue shock syndrome (DSS) and unusual dengue (UD) or

expanded dengue syndrome (EDS) . UF can not be diagnosed clinically, its diagnosis depend on virology or serology. DF is considered to be a mild disease because death is rarely reported, but massive bleeding may be associated with DF. DHF, clinical presentations during the febrile phase are similar to those in DF. The distinct feature of DHF is the increase in vascular permeability (plasma leakage) that differentiates DHF from DF. The plasma leakage is selective leakage into the pleural and peritoneal cavities that results in pleural effusion and ascites. DSS – presentations are the same as those in DHF but the plasma leakage is so severe that the patient develops shock. UD – most of the unusual cases are DHF cases with prolonged shock or DHF inpatients with co-morbidities or DHF together with other infections.

Most people with dengue have mild or no symptoms and will get better in 1–2 weeks. Rarely, dengue can be severe and lead to death. If symptoms occur, they usually begin 4–10 days after infection and last for 2–7 days. Symptoms may include high fever (40°C/104°), severe headache, pain behind the eyes, muscle and joint pain, nausea, vomiting, swollen gland and rash. Individuals who are infected for the second time are at greater risk of severe dengue.

Severe dengue symptoms often come after the fever has gone away which are severe abdominal pain, persistent vomiting, rapid breathing, bleeding gums or nose ,fatigue, restlessness, blood in vomit or stool, being very thirsty, pale and cold skin.

For patients presenting during the first week after fever onset, diagnostic testing should include a test for dengue virus which detects NS1 antigen IgM and IgG antibodies. These tests can range from rapid qualitative immunochromatographic tests, to ELISA and rRT-PCR. For patients presenting >1 week after fever onset, IgM detection is most useful, although NS1 has been reported positive up to 12 days after fever onset .

There is no specific drug for dengue. Most cases of dengue fever are treated symptomatically. Acetaminophen (paracetamol) is often used to control pain. Non-steroidal anti-inflammatory drugs like ibuprofen and aspirin are avoided as they can increase the risk of bleeding. For people with severe dengue, hospitalization is often needed.

So far one vaccine (Dengvaxia) has been approved and licensed in some countries. However, only persons with evidence of past dengue infection can be protected by this vaccine. Several additional dengue vaccine candidates are under evaluation.

Blog by Dr. Aditi Kumar