Nipah Virus in India: Antibodies Detected In Bats In Mahabaleshwar; Does It Pose A Threat? Here's What Researchers Found

Southeast Asian countries including India were potential hotspots for NiV disease a recent study found.

Mumbai: A survey to study the prevalence of Nipah virus (NiV) was conducted by the National Institute of Virology which is a part of the India Council of Medical Research.  The researchers found the presence of antibodies against NiV in some bat species from a cave in Mahabaleshwar. 

The Nipah virus which is usually found in bats is in the World Health Organisation's top 10 priority list of pathogens, rightfully so, because it has led to some deadly outbreaks in the recent past around the world. 

According to the study published in the Journal of Infection and Public Health titled - Detection of possible Nipah virus infection in Rousettus leschenaultii and Pipistrellus Pipistrellus bats in Maharashtra, India, the country first found evidence of NiV infection in the Siliguri district, West Bengal in 2001 followed by Nadia district in West Bengal in 2007. The presence of NiV antibodies were detected in the Mynaguri and Dubri district of Assam and Cooch Behar area of West Bengal, both places situated close to the Bangladesh border during earlier proactive studies. A third outbreak occurred in the Kozhikode district of Kerala in 2018 with 18 case fatalities, followed by another outbreak in the same state in 2019.

In a recent study, it was found that Southeast Asian countries including India were potential hotspots for NiV disease. 

The study on NiV in Indian bats

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.

In March 2020, the researchers trapped two species of bats, Rousettus leschenaultii (medium-sized fruit-eating bats) and Pipistrellus pipistrellus (tiny insectivorous bats) from a cave in Mahabelshwar using mist nets. Blood, throat, and rectal swab samples were collected onsite from anesthetized 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 in 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.

While speaking to TOI, Dr. Pragya Yadav, NIV scientist and one of the authors, said that none of the bat species in Maharashtra had previously shown exposure to Nipah.

"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", said the study.

Further investigations required

"The exposure of R. leschenaultii bats to NiV warrants further investigation as roosting and breeding habitats of the Rousettus spp. and Pteropus spp. vary greatly. 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", the researchers said.

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 appear remote, the study said.

"Presence of NiV RNA in the bat saliva poses a threat to humans."

Their positivity might be explained because they share the same habitat with R leschenaultii bats inside the cave.

They concluded that more studies will be required to understand thoroughly.

"However, it is 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 is very important to understand the bat ecology, seasonality of NiV and the transmission risks associated with it, for the one health approach."