Science for All Newsletter Why bats do not fall ill from the viruses they spread

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The world’s only winged mammals, nocturnal bats, of which there are some 1,500 species globally, have never quite got great press. Superstition has them down as bad omens. And science implicates them as the possible origins of the COVID 19 pandemic that killed seven million people globally, and in the outbreak of several other zoonotic diseases (that is, diseases that hop between animals and humans), including SARS (Severe Acute Respiratory Syndrome) in China, MERS (Middle East Respiratory Syndrome Coronavirus) in Saudi Arabia, Ebola in Africa, and Nipah in India.

So how do these animals, that have catalysed sweeping disease outbreaks among people around the world, not fall sick from the viruses they carry and transmit? Now a new paper in Science Advances untangles this conundrum.

Researchers studied the world’s largest family of bats, and found that they, unlike every single mammal in the world, possess two copies of genes that produce antibodies (proteins that help the immune system fend infections), and not just one.

“We’ve never seen anything like this in a mammal before,” said Hannah Frank, associate professor of ecology and evolutionary biology at Tulane University author of the study, in a release. This completely changes our understanding of mammalian immune systems “and raises exciting new questions about why bats have been so evolutionarily successful and how they respond to viruses,” he added.

For the study, the scientists looked at vesper bats, of which there are 500 species across the globe, except Antarctica. They studied the antibodies, which are protective Y-shaped proteins made of two heavy protein chains and two light protein chains. Unlike all other mammals, including humans, vesper bats have two separate heavy-chain gene systems, boosting their antibody diversity, they discovered.

To unravel the evolutionary origins of this duplication, the scientists studied genomes of 34 species of bats, including 26 closely related bats and found that the copy is present in every vespertilionid examined except the pallid bat, Antrozous pallidus.

How bats remain reservoirs of viruses without being infected by them could assist scientists understand immune responses among different species and help prevent disease spillover, said the paper. “It doesn’t fully explain why bats are such effective viral reservoirs, but it reveals a level of immune variety we didn’t know existed and gives us an entirely new direction to explore,” said Dr. Frank

In an older study, also published in Scientific Reports, researchers found that bats and coronaviruses have been evolving together for millions of years: this has produced different strains in different groups of bats around the world, it added. Scientists studied various coronaviruses in 36 bat species from the western Indian Ocean and nearby areas of Africa and found that different groups of bats had their own unique strains of coronavirus.

India is home to 135 species of bats, forming the largest order of mammals in the country, according to State of India’s Bats 2024-2025 published by the Bat Conservation International and Nature Conservation Foundation. Despite the critical role they play in ecosystems, by dispersing seeds, pollinating plants and preying on pest insects, “bats receive an insignificant amount of attention from the country’s research and conservation communities and scant recognition in government policies and programs,” this document said.

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