Coronaviruses that cause severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) are speculated to have originated in bats. But the mechanisms by which these viruses are maintained viable in individuals and bats remain an enigma.

A research team from the University of Saskatchewan (USask) in Canada has just uncovered how bats can carry MERS coronavirus without getting sick—a finding that could shed light on how coronaviruses make the jump to humans and other animals.

“The bats don’t get rid of the virus and yet don’t get sick. We wanted to understand why the MERS virus doesn’t shut down the bat immune responses as it does in humans,” said USask microbiologist Vikram Misra in a statement.

The team demonstrated in their research for the first time that cells from an insect-eating brown bat can be persistently infected with MERS coronavirus for months, due to important adaptations from both the bat and the virus working together.

“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 Misra, co-author. “SARS-CoV-2 (the virus that causes COVID-19) is thought to operate in the same way.”

Misra said the team’s work suggests that stresses on bats—such as wet markets, other diseases, and possibly habitat loss—may have a role in coronavirus spilling over to other species.

“When a bat experiences stress to their immune system, it disrupts this immune system-virus balance and allows the virus to multiply,” he said.

The research was carried out at USask’s Vaccine and Infectious Disease Organization-International Vaccine Centre (VIDO-InterVac), one of the world’s largest containment Level 3 research facilities, by a team of researchers from USask’s Western College of Veterinary Medicine and VIDO-InterVac.

“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 VIDO-InterVac scientist Darryl Falzarano, co-author of the study.

So far, the SARS-CoV-2 virus has infected more than 3.5 million people worldwide and killed 7% of those who tested positive. In contrast, the MERS virus infected nearly 2,500 people in 2012 but killed one in every three people infected. There is no vaccine for either SARS-CoV-2 or MERS.

Experts still aren’t sure what is the actual origin of the current COVID-19 pandemic. Since the virus is so similar to other viruses found in bats, it is likely that that’s where it originated, but so far, no smoking gun has been found yet. In order to confirm this theory, researchers need to isolate a live virus in a suspected species to correctly prove the source, and this hasn’t been done just yet.

The study was published in the journal Nature.