Dengue remains unconquered

Dengue started late this year in India due to a prolonged monsoon, but the dry spell seems to have set off breeding now and it may persist for a while if preventive measures are not taken. However, the total number of dengue cases reported this year is fewer than the number for the corresponding period last year. According to the National Vector Borne Disease Control Program, New Delhi, dengue has increased 300% across the country over the last decade.

We have so far been unable to develop specific drugs or line of treatment to thwart the dengue epidemic despite thousands of deaths across the country over the years. The real challenge in the development of vaccines is to synthesise a material that can induce protective immunity to all the four sub-types of dengue virus. However, that there are no vaccines or approved treatment against this deadly epidemic outbreak is a real challenge to citizens, the State and the medical-scientific community.

In 2017, the country suffered 1,88,401 dengue cases, compared to 60,000 in 2009. The World Health Organization (WHO) reported that nearly 100 million dengue infections occur annually around the globe. A pattern has been observed over the past five decades wherein the disease has spread 30-fold.

The southern states of Kerala, Karnataka and Tamil Nadu are concerned over higher deaths due to the incidence of dengue infections in the past five years. While Tamil Nadu and Puducherry witnessed a spike in dengue cases till November 2018, Karnataka reported only 1,903 cases. Reports of the union health ministry’s Directorate General of Health Services indicate that nearly 1,550 deaths and 5,98,687 cases were reported since 2010; among these 44,182 cases and 69 deaths were reported from Karnataka.

The dengue virus exists in four serotypes and its clinical manifestation and disease severity differ among them. Dengue fever complications include symptoms like sudden onset of fever, dehydration, abdominal pain, muscle and joint pain, nausea, fatigue and vomiting.

The journal Nature Reviews Microbiology explains the emergence of ancestral dengue virus which could be an additional serotype that is capable of spreading from non-human primates. So, evolution of new dengue infections and disease manifestations are expected.

The first clinically recognised dengue epidemics occurred almost simultaneously in Asia, Africa, and North America in the 1780s. In India, the first epidemic of clinical dengue-like illness was recorded in Chennai in 1780 and the first virologically-proven epidemic of dengue occurred in Kolkata and the eastern coast of India in 1963.

The dengue infection reminds mankind that nature is more powerful than science because no person is protected against this flavivirus, which spreads all over through the bite of the female Aedes aegypti mosquito. This dark mosquito with white streak can populate in natural habitats by laying eggs in stagnant water. The two types of commonly laid eggs, known as rapid hatch eggs and delayed hatch eggs have the ability to survive for a relatively long time and hatch during favourable conditions.

Heavy rainfall and subsequent water-logging is directly related to the spatial distribution of these mosquitoes. The hatching and embryonic development of Aedes aegypti mosquito eggs complete within 48-72 hours, which is a real threat for the control of Aedes aegypti population during the rainy season. Every year, rainfall facilitates the breeding of Aedes aegypti, which contributes to the outbreak of the dengue menace throughout the country. Vector density is directly proportional to viral transmission.

Though several factors like host genetic factors, previous exposure to any serotypes or sub-categories and post-infection care play a crucial role in deciding the severity of dengue infection, no consensus is reached on disease severity and serotype variation. Research on efficient virus neutralisation methods is currently progressing to meet the needs of infected patients.

Today, doctors attempt to tackle the epidemic with intravenous fluids, oral rehydration therapy, and blood transfusions. Early diagnosis using advanced techniques like Real-Time Polymerase Chain Reaction, IgM Enzyme-linked Immuno Sorbent Assay and integrated vector management will have a sure impact on incidence of dengue.

The realities that confront the medical community to combat the epidemic are uncontrolled migration of population, unplanned housing, poor sanitation and improper water dispersal and disposal management systems. Therefore, the need to create awareness among the people about the transmission kinetics of this deadly virus will help the medical community and civil society to control and contain this viral infection.

Clearly, community participation from the private sector and public agencies is the only solution to tackle the deadly dengue virus. As the transmission of the deadly virus revolves around the human-to-mosquito-to-human cycle, better sanitation and mosquito control practices are the immediate need of the hour to control Aedes aegypti mosquitoes.

(The writer is Assistant Professor, Department of Life Sciences, CHRIST Deemed to be University, Bengaluru)