Scientists at Pune’s Indian Council of Medical Research – National Institute of Virology were able to detect the presence of IgG antibodies against Nipah virus infection (NiV) in 51 bats that were captured from Karnataka, Kerala, Tamil Nadu and Puducherry.
Nipah virus (NiV) is one of the priority pathogens with a pandemic potential. Though the spread is far slower than SARS-CoV-2, case fatality is the biggest concern. The sudden emergence of Nipah in Kerala, during 2018–2019 has been astonishing with respect to its introduction in the unaffected areas, scientists said.
The fruit bats of genus Pteropus are identified to be the main reservoir of the Nipah virus causing annual outbreaks in Malaysia, Bangladesh and other countries in South-East Asia including India. However, three incidences of NiV infections in humans in Kerala which is far distant from the known “Nipah belt” in consecutive years with no identified intermediate animal host or confirmed mode of entry into human population warrants the heightened need of constant surveillance of NiV in bats, animals and humans, researchers with ICMR-NIV said.
The sequence analyses showed its deviation from the NiV strains from Bangladesh and northeastern region of India. Analysis of NiV N gene sequences from the new hotspots in Kerala also suggested the presence of a new genotype independently evolving in southern India. Hence, knowledge of the distribution and movement patterns of bat species that act as the reservoir hosts of Nipah virus was necessary to identify the regions at risk, and possible events of spillover, scientists added.
Considering all these factors, a countrywide survey of Nipah virus in Pteropus bats was undertaken. The aim was to determine presence of NiV activity in bat populations in southern states and union territories which are geographically close to the new hotspot of NiV and a state (Odisha) bordering West Bengal in the southeast.
Scientists Mangesh Gokhale, A B Sudeep, D T Mourya, Pragya Yadav and others have published the findings of this study in a letter to editor titled `Serosurvey for Nipah virus in bat population of southern part of India’ in Comparative Immunology, Microbiology and Infectious Diseases recently.
A total of 573 throat swabs/rectal swabs of P. medius (n = 541) and R. leschenaultii bats (n = 32) and blood samples of P. medius bats (n = 255) were collected from Telangana, Kerala, Karnataka, Tamil Nadu, Odisha and Puducherry during January-November 2019. Throat/rectal swab specimens of P.medius and R. leschenaultii bats were found negative for the Nipah virus infection.
However, anti-NiV IgG antibodies were detected in serum samples of Pteropus bats collected from Karnataka (24/76), Kerala (18/113), Tamil Nadu (7/26) and Puducherry (2/21). High antibody prevalence of 20 percent was detected in Pteropus bat species according to the study. Anti-NiV IgG antibodies couldn’t be detected in Pteropus serum samples collected from two sites in Dhenkanal, Odisha.
Earlier ICMR-National Institute of Virology, Pune conducted Nipah surveillance among bat populations in northeastern states of India during 2015. The surveillance revealed the presence of NiV among P. medius bats collected from Cooch Behar district, West Bengal and Dhubri district, Assam. Similarly, Nipah surveillance was carried out amongst the pig population of eight districts of Mizoram state in the northeast. However, all the pig serum samples tested negative for anti-Nipah IgG antibodies.
The first human infection with NiV was identified during an outbreak of severe encephalitis in Malaysia in 1998–1999. Both animal-to-humans and human-to-human transmission has been documented during different outbreaks. More than 700 human cases of Nipah virus infections were reported from Malaysia, India, Bangladesh, Singapore and Philippines during 1998− 2018. India has witnessed four outbreaks of Nipah virus disease during 2001–2019. The first outbreak of NiV with presentation of febrile illness and neurological symptoms was observed among the human population in Siliguri, West Bengal during 2001 with a case fatality rate (CFR) of 74%. Subsequently, an outbreak was reported from Nadia district in West Bengal in 2007 which affected five people and all succumbed to infection.