Can bats spread Nipah virus? Experts allay concerns

After the recent confirmation of the presence of the Nipah virus (NiV) in Kerala and the death of a 12-year-old boy, fear about transmission from bats that arose in 2018 is visible among people again.
Flying foxes bats
Flying foxes bats
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Numerous flying fox bats can be seen hanging from a tree located in Thiruvananthapuram’s Thirumala. The tree is situated on a road on which many people go for a walk in the morning and evening. Last week, when some people from the locality met for a morning walk, they began a discussion about this tree and the bats, in the wake of the confirmation of the presence of the Nipah virus (NiV) again in Kerala.

Sixty-seven-year-old Muralikrishna, a retired central government employee, pointing to the tree said, “Should we ask the authorities to cut down the tree? There are so many fruit bats, how can we walk here peacefully?” Replying to him, retired doctor Ananthakrishna said, “Don’t be foolish, as per the World Health Organisation, if bats are stressed it might cause a spillover [virus moving from one species to another]. These birds are full of viruses, they can shed it anywhere.” All these opinions created tension among those around them.

It was in May 2018 that the fear of bats grew in Kerala, after 17 of the 19 infected people in Kozhikode and Malappuram districts succumbed to the Nipah virus. A year later, NiV reappeared in Ernakulam in June 2019. This year, the virus was reported for the third time in the state in Kozhikode a week ago, and a 12-year-old boy lost his life. Fortunately, all the boy’s primary contacts tested negative. But the fear of bats still persists in the state, especially among people who have bats living around them.

NiV was first detected in Malaysia’s Kampung Sungai Nipah in 1998. In 2001, it appeared in Bangladesh, and the same year the virus infected 65 people in Siliguri, West Bengal, India. Among these, 45 patients died. Though there are studies that say that the source of the infection in Malaysia was pigs, in India the source has not been determined yet.

No proof but still bats are vilified as carriers

Bats are considered to be natural hosts of the virus. However, when NiV struck in 2018 though bats were present around the areas where the infection occurred in Kozhikode, none of the bat samples collected tested positive for the virus. It was found that bats were present in the well from which the family of the first three victims used to fetch drinking water. But experts said that they were bats that feed on insects and were not carriers of the virus.

“There is no credible evidence that bats harbour more viruses, or even more deadly viruses than other animals. Frightening headlines in the media have the potential to jeopardise decades of conservation progress,” Merlin D Tuttle, founder and Executive Director, Merlin Tuttle’s Bat Conservation and Research Fellow, Department of Integrative Biology, University of Texas at Austin, told TNM.

“Transmission of viruses from bats to humans is exceedingly rare. For anyone who simply doesn’t handle them or consume unpasteurised palm juice or unwashed fruits, the odds of contracting any disease from a bat are extremely remote. The benefits of sharing our neighbourhoods with bats far outweigh any risks. Even in the case of Nipah, the odds of being infected by another human dwarf those of getting it from a bat!” he added.

The renowned chiropterologist said that Nipah can be harboured in a wide variety of animals, including domestic ones. Until now there is no proof or study that substantiates the role of bats in the NiV outbreak in India.

“Just being able to survive a disease does not make an animal an important source of transmission to humans. In Austin, Texas, where I live, we share the city with millions of bats who routinely come into close contact with humans. And despite proof that some harbour rabies, no one in the more than 100-year history of our city has contracted this or any other disease from a bat,” he said.

Arakkal Madhavan, who has been studying bats for more than 50 years and is probably Kerala’s first chiropterologist, said that no conclusion can be drawn without proving the source of the infection scientifically. “I’m not blatantly rejecting any speculation. But as the saying goes ‘give a dog a bad name and hang him’, that is the situation bats face,” he said.

Tuttle pointed out that more viruses have been found in bats because studies haven’t similarly sampled other animals.

Until Nipah, a lot of people used to consume bat meat. “There are still people who consume its meat. It’s believed to help asthma patients, but no one has been infected,” Madhavan added.

The theory of virus spillover by bats when they are stressed has also not been proven yet. Researchers pointed out that there has been habitat destruction at many places around the world but there is no proof of virus spillover by bats.

Bats play a crucial role in environment

“In a rush to judgement, the historic rarity of viral spillover from bats to humans has been largely overlooked. We have a long history of co-association. If bats were as dangerous as postulated, why has it been impossible to document major disease outbreaks among the millions of African, Asian and Pacific Islanders who eat them? Why have there been no significant disease outbreaks in cities of Africa, Australia, and the United States where millions of bats live in close association with people?” an article by Tuttle says.

Madhavan says that bats have a very important role in our ecosystem.

“Bats are actually friends of nature. They play a crucial role in pollination. They eat insects that destroy our crops, they are also material for a wide range of research,” he added.

Tuttle also pointed out how bats are significant to our ecosystem and in turn to the economy. “Researchers in Indonesia conservatively estimate that bats save cacao growers more than $700 million annually in avoided insect damage. In Mexico, tequila and mescal production worth billions annually relies on bats that pollinate agaves. From Southeast Asia to the Mediterranean, bats provide key pest control for rice growers. In South Africa, macadamia growers benefit from bat control of stink bugs,” he says in another article.

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