CHENNAI: A seroprevalence study conducted by the State Public Health Laboratory, Directorate of Public Health and Preventive Medicine during Covid-19 in December 2021 has showed that the dengue disease burden was low during that period, possibly due to the IgG antibodies for Covid-19 that causes SARS CoV-2 virus having a neutralising effect against the dengue-causing virus.
The officials said further study is needed to prove the possible viral interference between SARSCoV-2 and dengue virus. The authors said the 2021 study will be helpful for the public health officials to focus on one particular infectious disease during an outbreak, rather than focussing on less important ones.
The state-wide cluster-randomised community-based study conducted by the Directorate of Public Health and Preventive Medicine, led by Dr T S Selvavinayagam, who is also the chief author, was published this month in PLOS Global Public Health, a journal for public health research.
In the study, the dengue burden in the community was found out by the seroprevalence. The study also found out the percentage of people in the population who have anti dengue antibodies, Dengue IgM which shows an ongoing infection at the time of study, and Dengue IgG antibodies, which shows past infection.
The study found that the seroprevalence of dengue was very low in the community with 4.12 % for Dengue IgM and 6.4% for Dengue IgG. Similarly only 3.76 % of the female Aedes mosquito pools were positive for dengue virus. In comparison, a similar study conducted by ICMR-National Institute of Epidemiology, Chennai in 2017, showed Dengue IgG to be very high at 77%.
The anti-SARS-CoV-2 IgG antibody level meanwhile remained high (87.3%) during the 2021 study. The researchers said during Covid-19 when they saw low dengue cases, they thought it could be due to under-reporting of cases.
While there were a few studies earlier that said dengue cases were low during Covid-19, DPH officials said this is the first study to prove dengue cases were low in both humans and mosquitoes.
The researchers said this could be because of Covid-19 antibodies blocking the entry of dengue virus. Further, studies needed to prove this hypothesis, they added.