Nipah outbreak: ‘Driving away bats is not the answer’

What explains the sudden, recent emergence of Nipah in Kerala when bat species that carry the virus have been living in proximity to human settlements for hundreds of thousands of years?

Nipah’s recent emergence in Kerala is a million-dollar question. The known carrier of the Nipah virus, the Indian flying fox (Pteropus medius) is a common and ubiquitous bat species. Added to it is the fact that the Indian flying fox is a commensal species too [that is, carriers of pathogens that may not affect the bat].

So, theoretically any place in India is potentially a Nipah-prone region. [Recent research by the National Institute of Virology found evidence of Nipah virus in the bat population in nine States.] Nipah cases were reported in West Bengal in 2001 and 2007. Kerala’s detection of Nipah cases since 2018 could be because its better healthcare system responds quickly. But this needs to be further investigated, particularly why it is recurring here. Moreover, in Kerala, it has not been conclusively proven that the index patient (patient zero) contracted the virus by consuming fruits contaminated by bat saliva or through contact with bat shedding.

Do you see a pattern in the outbreaks as being related to, perhaps, bat densities?

Four incidents have occurred in Kerala since 2018, primarily around Kozhikode district, with a few cases in Malappuram and Ernakulam districts. When it comes to the bat population, there is nothing specific to Kozhikode that could make it more susceptible to Nipah. There are bigger fruit bat roosts in other parts of the State.

There have been two outbreaks each in June and September. Do the monsoons have something to do with it? One hypothesis is that when the animals are stressed, they could be expelling more viruses. But we are yet to figure out if the south-west monsoon or breeding season causes stress for bats.

Are these stressors for bats on the rise, considering increased human-wildlife interaction?

We have destroyed forest habitats and encroached upon them, bringing humans closer to wildlife. Close proximity to bats may be giving them additional stress, leading to greater spillover possibilities.

Preliminary studies done by those in our university have shown that climate change also impacts bats in Kerala. [A 2020 research paper at the institute showed a complete loss of suitable habitat for the endangered Latidens salimalii that is endemic to the Western Ghats when effects of global warming are extrapolated.] However, we need more studies to understand how climate change affects individual bat species.

We have only observed the loss of habitat, but there is no comprehensive understanding of the status and distribution of flying foxes. We recently launched a mobile app that allows citizens to record roost sites and take count of flying foxes. We hope to document these through citizen science.

The Nipah outbreak seems to have amplified the fear around bats, with reports of bat habitats being disturbed intentionally. Are these effective as a precautionary measure?

Since the first Nipah outbreak in 2018, there has been a tendency to destroy the fruit bat roosting trees. The majority of these roosting trees, unfortunately, are located near the human-dominated landscape. Their destruction, however, further endangers public health as it can result in fruit bats moving sporadically and widely anywhere and everywhere, thus putting them in contact with many more people than would otherwise have been the case.

But, driving away bats is not the answer. Bats perform important ecological functions and have benefits for humans. For example, fruit bats, which do carry Nipah, also perform important pollination services. Banana plants and mango and cashew trees, to name a few, rely on bats for pollination. Fruit bats are also important in the dispersal of seeds of several species. The insect bats eat huge quantities of insects and effectively control pest populations that would have otherwise caused severe damage to crops.

This is why the One Health approach (a multidisciplinary approach that combines medicine, ecology, and other fields to tackle health as an issue of humans, wildlife, and their shared environment) becomes so important. It is also important to ensure that bat roosts are not disturbed, for reasons beyond ensuring human health.

Would mass sero-surveillance of bats to detect outbreaks before they happen help? For instance, Nipah antibodies were recently found in Wayanad among bats, despite there being no reported human cases.

We have been missing opportunities, at least now we should seriously think of constituting a multidisciplinary team and should conduct mass sero-surveillance.

At the Kerala Agricultural University, we have been undertaking studies on bats for three decades. One approach paper was published soon after the 2018 outbreak [the paper, “Prioritising surveillance of Nipah virus in India”, was published in Plos Neglected Tropical Diseases in 2019]. The team of researchers from across the globe did an extensive survey of literature and analysed them using machine learning techniques. It concluded that 11 Indian bat species had been identified as having antibodies that react to Nipah virus serological tests. Seven of these species are found in Kerala. However, in the process of finding literature on bats and Nipah, there was a lack of studies from India.

While Kerala has experienced its fourth outbreak, we are still speculating how and when the spillover [of disease from bat to human] happens. Figuring this route of transmission is key. In Malaysia and Bangladesh, researchers clearly identified how the viruses could be transmitted. They took precautionary steps there. It becomes important to identify the spillover mechanism.

It does seem like bats do not get the sort of research attention they deserve.

Yes, unfortunately, very little research happens on bats in India and in Kerala. The reasons for that could be many. It is hard to study them: they are nocturnal, and capturing them is not easy for further studies on, say, their acoustics. They are also less charismatic compared to tigers and elephants and [that] could be deterring many from specialising in the study of bats. We don’t understand many critical things about bats. We don’t understand how diseases spill over. There are even gaps in basic studies of bats, including the taxonomy, ecology, and biology of bats.