Why do bats play host to so many viruses?

Bats harbor many viruses that can spill over into humans, including Marburg, Ebola, and famously SARS-CoV-2. But while these viruses often cause severe illness in humans, they do not appear to hamper bats. A new study offers a clue to why bats can tolerate so many viruses that can be fatal to humans. Researchers led by Michael Hiller at the LOEWE Centre for Translational and Biodiversity Genomics and Aaron T. Irving at Zhejiang University found that bats have more immune system modifications compared with other mammals ( Nature 2025, DOI: 10.1038/s41586-024-08471-0 ). The researchers performed comprehensive genome sequencing on 10 bat species that are known reservoirs of zoonotic viruses. Comparing the sequences with those of 115 other mammal species, they found that bats display immune signatures not found in other mammals. The group paid particular attention to the gene for the protein ISG15. This protein plays a role in the