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On the edge: Bats in northeast India found to carry filoviruses that could spread to humans

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1 Nov 2019
On the edge: Bats in northeast India found to carry filoviruses that could spread to humans

Sometime in the middle of October each year, the Bomrr clan in Nagaland rush to the caves in Mimi village. With a good stock of burning firewood, men and women are ready for the bat harvest festival—an annual ritual where anywhere between 7,000 to 25,000 bats are suffocated or smashed to their deaths. These bats, the clan believes, have medicinal properties and can cure diseases like diarrhoea and body ache, and increase vigour. Now, a new study has shown that these bats, rather than being a cure to diseases, carry deadly filoviruses that could infect humans.

Filoviruses are a group of viruses known to cause hemorrhagic diseases in humans and primates. The Ebola virus and Marburg virus are some of the infamous filoviruses that have caused deadly epidemics globally. Bats, found in most parts of the world, are known to carry these filoviruses and act as a reservoir. Activities like bat hunting and mining, which bring humans in close contact with bats, pose a high risk of transmission of these viruses to humans.

In the current study, researchers from the Duke-National University of Singapore Medical School, Singapore and the National Centre for Biological Sciences (NCBS), Bengaluru, along with collaborators from the USA and China, have detected specific antibodies that are reactive to filoviruses in blood samples of a few bats and people participating in the harvest festival. The study is published in the journal PLOS Neglected Tropical Diseases and was partially funded by the Department of Atomic Energy, Government of India.

“We know bats are important reservoirs of zoonotic viruses and the discovery of this bat harvesting practice by my collaborator, Pilot Dovih from NCBS, represented a unique study site,” shares Dr Ian Mendenhall, in an interview with Research Matters. He is a Principal Research Scientist at the Duke-National University of Singapore Medical School and the corresponding author of the study. “Being able to study both bats and humans allowed us to detect if these groups had been exposed to the same filoviruses,” he adds.

During the bat harvesting festival, the participants come in contact with the saliva, blood and excreta of predominantly two bat species—Rousettus leschenaultii (Leschenault's rousette) and Eonycteris spelaea (Cave nectar bat). The researchers collected blood samples from specimens of these two species of bats and 85 individuals who participated in the annual festival. They also gathered information regarding the gender, age, occupation and the number of times the individual participated in bat hunting.

A basket of bats that have been killed and will be distributed to the community. Image Credits - Dr. Zavei Heise

The blood sera samples of bats and humans were analysed to find antibodies that are reactive to filoviruses, which indicate previous exposure to these viruses. The study found that five human samples and five bat samples had antibodies reactive to filoviruses.

“Interestingly, one species of bats had the same serological reactivity profile as humans against a panel of filovirus proteins. This observation indicates this species may be the source of human exposure. There also appears to be multiple filoviruses circulating in bats in this region, but we do not know if these viruses are pathogenic or dangerous,” explains Dr Mendenhall. Besides, a majority of bat hunters were males between 18 to 50 years of age and had participated at least eleven times in the harvest.

Previous studies from Singapore, Southeast Asia and China have found widespread evidence of filovirus exposure in bats species that are harvested in northeast India. However, there is more to understand about their diversity and transmission. “There appears to be significant filovirus diversity, demonstrating our knowledge gaps about this virus family. Our results emphasise the need to understand filovirus ecology and diversity in this region better,” asserts Dr Mendenhall.

Although there is no evidence of previous filovirus outbreaks in northeast India, the study shows that people involved in bat harvesting were exposed to filoviruses. What led to this exposure is something scientists are yet to figure out. Is this region on the brink of a possible epidemic?

“We do not know if there is a chance of an epidemic in this region because we don’t understand the nature of these viruses,” says Dr Mendenhall.

The researchers hypothesise that there is no such outbreak yet because of various reasons. The virus may have had trouble replicating in humans, or there could be ecological barriers preventing transmission to humans, or the transmitted filoviruses could be causing infections in humans without any symptoms.

The researchers add that there is no cause of concern or panic as yet and awareness is what we need.

“Our study reinforces the need to sample in high-risk human-animal interfaces where virus spillover may occur. Part of our study also involved educating the harvest participants about potential risks and the importance of bats to the ecosystem. We are continuing our work in northeast India to identify these viruses and better understand their risk to public health,” says Dr Mendenhall. “Bats are important to the ecosystem as they consume pests, and act as pollinators and seed dispersers. These findings shouldn't be used to motivate the destruction of bats out of fear,” he concludes.