In 2019, when Nipah surfaced in the State for a second consecutive year, experts had warned that given the omnipresence of the Pteropus medius species of bats, found to be the key reservoirs of Nipah virus (NiV) across the State, Kerala should probably expect annual outbreaks of Nipah, and not necessarily in the same location or with the same symptom profile.
As the State battles its fourth brush with Nipah, despite the expertise in launching a formidable outbreak containment effort when the virus surfaces, the State has failed to invest in disease epidemiology which is crucial in understanding and preparing for this zoonotic infection with high case fatality.
Except in 2019, when a lone case of Nipah was reported in Ernakulam, all three outbreaks have been in Kozhikode, that too in locations situated not very far from each other. The question that has been prime on everyone’s mind is why have the virus spillover events been recurring in the same belt in Kozhikode even though Pteropus bats are seen everywhere?
Bats and humans have coexisted over the past 2,000 years. It is also common knowledge that they are the key reservoirs of many pathogens, including NiV. In the previous Niv outbreaks in Malaysia and in Bangladesh, scientists could establish a clear route of transmission of the virus from bats to humans.
“Though this is our fourth NiV outbreak, we are still riding on speculations as to how or when the virus spillover occurs or what could be the spillover route. How did the index case contract the virus on each of these occasions? That the human could have contracted the virus by consuming fruits contaminated by bat saliva or through contact with bat sheddings is just a premise and not a proven scientific fact,” points out P. O. Nameer, Dean, College of Climate Change and Environmental Science, KAU, Thrissur.
“A study on NiV dynamics in bats is essential to establish why and how the virus spillover episodes occur; if there is a specific time frame and if geography or climate change plays a role in these events. Given that NiV is a highly fatal pathogen and one included in the WHO’s list of priority pathogens, Kerala should undertake systematic surveillance of the bat species as well as studies on the ecological dynamics of NiV and the epidemiology of spillover transmission to humans,” says Dr. Nameer.
Yet, as soon as one outbreak subsides, the health system’s priorities shift and research takes a back seat
“After the outbreaks in May 2018 and June 2019, it was our assumption that outbreaks usually coincided with the breeding season of bats (it was assumed to be from December to May), when the virus replicates in bats and that the virus spillover happens during this stressful period. But with outbreaks happening in September (2021) and the current one August, we are no longer sure if seasonality of outbreaks can be predicted,” says R. Aravind, Head of Infectious Diseases, Govt. MCH, Thiruvananthapuram.
However, breeding season should be seen as just one of the reasons for virus spillovers and climate change, ecological factors or loss of habitat can all act as stressors at any point in time, it is pointed out.
Essentially, one has no control over the natural spillovers of infection in the environment and it is impossible to ensure zero Nipah, just by staying away from bats.
The health system’s priority should be on ensuring that there is zero human to human transmission by strengthening disease surveillance, analysing unusual deaths in the community and maintaining strict infection prevention policies in hospitals.
