ICMR-NIV survey finds proof of Nipah virus in bats across nine states, one UT

Nipah virus causes a highly fatal respiratory and encephalitic infection in humans. The Pteropus species of fruit bats, commonly called flying foxes, are the known carriers of the virus. One of the priority pathogens with a pandemic potential, case fatality is a big concern and Nipah’s sudden emergence in 2018-19 in Kerala had warranted the need for constant surveillance.

In the past, the ICMR-NIV identified the presence of Nipah virus in fruit bats across Dhubri district of Assam; Myanaguri and Cooch Behar area of West Bengal and Kerala’s Kozhikode district. Scientists are carrying out a nationwide survey to find out the prevalence of the virus in different parts of the country. Dr Sheela Godbole, director-in-charge of ICMR-NIV, told The Indian Express that there was an absence of information on the status of the virus prevalence among the Pteropus bats in the rest of the country and hence, a decision was taken to conduct a nationwide survey.

The presence of antibodies indicates evidence of the virus circulation in the past in the bat population and according to Dr Yadav, the study will help identify areas at risk of spillover. “This will help in taking necessary precautionary steps to prevent future outbreaks in the country,” Dr Yadav added.

India reported its first outbreak in West Bengal’s Siliguri in January-February 2001 with 45 deaths among 66 cases. Those infected with the virus exhibited symptoms such as fever, headache, myalgia (pain in the muscles), vomiting, altered sensorium, acute respiratory distress, and convulsions. India then lacked the containment facilities to handle high-risk pathogens and diagnostic tests to detect the outbreak. It took support from USA’s Centers for Disease Control for diagnosis and could confirm the outbreak in 2006.

With the establishment of the BSL-3 facility at ICMR-NIV Pune in 2005, India could quickly detect the second outbreak of the Nipah virus in West Bengal’s Nadia district in April 2007.

In May 2018, the third outbreak of the Nipah virus claimed 16 lives among 18 confirmed cases reported from Kerala’s Kozhikode district. This was the first Nipah virus outbreak in southern India.

One quick result, in the aftermath of the Kerala experience, was the development of a point-of-care test for the Nipah virus– the first of its kind in the world by Dr. Yadav and her team.

With the isolation of the NiV, IgM, IgG ELISA for humans and IgG screening assay for bats and pigs were developed and used for the NiV surveillance. The seroprevalence among close contacts during the 2018 outbreak was found to be very low. Only three contacts showed IgM and IgG positivity out of 239. In June 2019, there was a fourth outbreak in the Ernakulam district of Kerala, with only a single case positive for Nipah virus who had fever and showed encephalitis-like symptoms. The patient survived with supportive care. None of the close contacts showed any seropositivity during the 2019 outbreak.

The last Nipah virus outbreak was reported in August-September 2021 in Kozhikode, with one person succumbing to the disease.

“In all three outbreaks, the Pteropus medius bats were positive [either by real-time or ELISA] near the index case house, pointing to the probable source of infection and transmission being bats. Surprisingly, in 2018, the disease was reported from a geographically distant area—in Kerala, where the outbreak was highly fatal. The outbreak investigation in the affected area by ICMR-NIV identified the presence of the Nipah virus in fruit bats,” Dr Yadav recalled.