How bats live with coronaviruses

Bats have evolved an intrinsic immunity to coronaviruses that stops them from getting sick, though they still carry the disease.

New research shows that the coronavirus that causes Middle East Respiratory Syndrome, or MERS — a virus similar to the one responsible for the current COVID-19 pandemic — stays in bats for a long time. But the flying mammals have evolved ways to render it mostly harmless.

“Instead of killing bat cells as the virus does with human cells, the MERS coronavirus enters a long-term relationship with the host, maintained by the bat’s unique ‘super’ immune system,” said Vikram Misra, a microbiologist at the University of Saskatchewan and one of the co-authors of a study published recently in Scientific Reports, in a press release.

SARS-CoV-2 — the virus that causes COVID-19 —” is thought to operate in the same way,” Misra said.

Misra and his colleagues found that big brown bats (Eptesicus fuscus) infected with MERS carried the disease for months, but the virus didn’t shut down the bats’ immune responses. The bats seemed unharmed, at least until diseases, habitat loss or stresses involved with wet markets compromised their immune systems.

“It disrupts this immune system-virus balance and allows the virus to multiply,” Misra said.

These same stresses that upset this balance in bats may also play a role in the disease spilling over into other species. Bats are suspected of being a source of MERS and other coronaviruses, though the viruses often pass to other intermediate hosts before jumping to humans. MERS is known to have jumped to camels before infecting humans.

“We see that the MERS coronavirus can very quickly adapt itself to a particular niche, and although we do not completely understand what is going on, this demonstrates how coronaviruses are able to jump from species to species so effortlessly,” said co-author Darryl Falzarano, a scientist from the University of Saskatchewan’s Vaccine and Infectious Disease Organization—International Vaccine Centre.

The study also notes that other problems, such as the fungus Pseudogymnoascus destructans that causes white-nosed syndrome in bats, can lead to an increase in MERS virus replication.