Study shows low dengue prevalence during COVID-19 in Tamil Nadu

Currently 75% of fever cases are due to flu viruses, says DPH

As many as 75% of people, who are treated for fever currently, have been diagnosed to have contracted flu viruses, according to the Directorate of Public Health. The incidence of dengue is under control and there has been a source reduction of Aedes mosquitoes that transmit dengue.  

To determine the reasons for the low prevalence of dengue during the COVID-19 due to the possible viral interference, the Department of Public Health and Preventive Medicine and State Public Health Laboratory, Chennai, conducted a community-based, cluster randomised sero-survey amid the pandemic in December 2021 to compare the antibody levels (seroprevalence) against DENV and SARS CoV-2 in the state. 

The study ‘Attrition in serum anti-DENV antibodies correlates with high anti-SARS-CoV-2 IgG levels and low DENV positivity in mosquito vectors—Findings from a State-wide cluster randomized community-based study in Tamil Nadu’, published in the recent issue of PLOS Global Public Health, ascertained the dengue burden in the community by the seroprevalence of anti-DENV antibodies in humans and by detecting the dengue IgM and IgG antibodies by Elisa and circulation of DENV in the vector mosquitoes by RT-PCR method. The study was done across all the 38 districts of the State with a population of 72 million.  

A total of 5,577 human serum samples from 186 clusters and 13,464 mosquito pools were collected from the environment and subjected to detailed laboratory investigations, said the study’s principal author and director of Public Health T.S. Selvavinayagam. 

“The results clearly demonstrated that the seroprevalence of dengue was very low in the community with 4.12% for DENV IgM and 6.4% for DENV IgG. A similar study, which was conducted by National Institute of Epidemiology, Chennai in 2017, found that dengue IgG was very high at 77%” he said.  

Similarly, only 3.76% of the female Aedes mosquito pools were positive for DENV. While anti-SARS-CoV-2 IgG antibody level remained high at 87.3%, the decline in dengue incidence and/or prevalence during COVID-19 pandemic (2020-22) appears to be attributed to possible viral interference and the neutralising effect of SARS CoV-2 IgG against DENV, the findings showed, Dr. Selvavinayagam added. 

The study further stated that integrated mosquito-human sampling across a specific geographical area could help assess the spatial seroprevalence pattern and assist identification of hot-spot regions of vector circulation. Such regions could be closely monitored and appropriate vector control measures to prevent outbreaks implemented.

While dengue and SARS-CoV-2 continue to remain major global public health concerns, predominantly in India, the dengue case incidence is exponentially increasing annually, and there is an ongoing geographical expansion of transmission areas and cocirculation of multiple DENV serotypes.  

It is important to establish laboratory-based sentinel surveillance with coordinated entomological and molecular surveillance for early diagnosis, prevention, and control of arboviral infections, the study concluded.

Published - November 25, 2024 08:32 pm IST