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Explained: In bats in Mahabaleshwar cave, antibodies against Nipah virus

Till date, India has experienced four episodes of NiV outbreaks with CFR ranging from 65% to 100%. The first evidence of NiV infection was reported in Siliguri district, West Bengal in 2001, followed by Nadia district in West Bengal in 2007.

Written by Anuradha Mascarenhas | Pune |
Updated: June 27, 2021 8:32:14 am
NiV is on the top-10 priority list pathogens identified by the World Health Organization.

A cross-sectional survey by Indian Council of Medical Research- National Institute of Virology to study the prevalence of Nipah virus (NiV) in bats of India has picked up samples with the presence of antibodies against the Nipah virus in some bat species from a cave in Mahabaleshwar, a popular hill station in Satara district, Maharashtra.

NiV is on the top-10 priority list pathogens identified by the World Health Organization.

Till date, India has experienced four episodes of NiV outbreaks with CFR ranging from 65% to 100%. The first evidence of NiV infection was reported in Siliguri district, West Bengal in 2001, followed by Nadia district in West Bengal in 2007. The presence of NiV antibodies were detected in Mynaguri and Dubri district of Assam and Cooch Behar of West Bengal, both places situated close to Bangladesh border . A third outbreak occurred in Kozhikode district of Kerala state in 2018 with 18 case fatalities, followed by another outbreak in the same state in 2019 . A study in 2018 has identified many South East Asian countries including Indian states as potential hotspots for the NiV disease.

Pteropus medius bats, which are large fruit-eating bats, are the incriminated reservoir for NiV in India as both NiV RNA and antibodies were detected in the samples of these bats collected during previous NiV outbreaks. Studies on other species of bats as potential NiV reservoirs in India are very limited.

The new study — Detection of possible Nipah virus infection in Rousettus leschenaultii and Pipistrellus Pipistrellus bats in Maharashtra, India, published in the Journal of Infection and Public Health — has found the virus and antibodies in different species. During March 2020, from a cave in Mahabaleshwar, two species of bats, Rousettus leschenaultii (medium-sized fruit eating bats) and Pipistrellus pipistrellus (tiny insectivorous bats), were trapped by researchers using mist nets.

Blood, throat and rectal swab samples were collected onsite from anaesthetised bats. Throat and rectal swab specimens were collected from all the bats. Necropsy of ten bats of each species was performed at the containment facility of Indian Council of Medical Research- National Institute of Virology (ICMR-NIV), Pune.

RNA was extracted from samples and Anti-NiV IgG antibodies were detected in a number of the samples. One bat each from R leschenaultii and P pipistrellus species tested positive for both NiV RNA and anti NiV IgG antibodies, the study said. This is the first report of possible NiV infection in R leschenaultii bats in India, which was demonstrated by the presence of both NiV RNA and anti-NiV IgG antibodies in bats, said Dr Pragya Yadav, NIV scientist and one of the authors.

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The cross-sectional survey was initiated to study the prevalence of NiV in bats of India by random sampling of P medius, R leschenaultii and P pipistrellus bats that have wide prevalence in India, said Mangesh Gokhale, lead author of the study, and Dr D T Mourya, former director of NIV and one of the authors.

In earlier investigations during the last decade, NiV activity could not be detected in R leschenaultii, despite processing several hundred bats including bats from the same location.

The exposure of R leschenaultii bats to NiV warrants further investigation as roosting and breeding habitats of the Rousettus and Pteropus vary greatly, the scientists said. More studies in bats and humans are therefore needed to understand the prevalence of the virus in the state.

The roost which was sampled was age-old and the virus might have been circulating among the inhabitants at low levels and not detected during earlier studies. Alternatively, a new introduction might have occurred from P medius to Rousettus bats through NiV-contaminated fruits, as both share the same fruit trees.

NiV detection in P pipistrellus bats, an insectivorous species, and their role in virus spill-over to humans appears remote, the study said. Their positivity might be explained through sharing the same habitat with R leschenaultii bats inside the cave.

Researchers said it was difficult to infer any conclusion as only a few bats were screened during the present study. Recurring outbreaks, high case fatality rate, human-to-human transmission and lack of effective vaccine/antivirals pose a major concern in India as bat roosts are very common in areas where large human populations reside, it said.

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