A survey of nearly 90 years of experimental infections shows some viruses are bad for bats
Even bats aren’t immune to taking a “sick day.”
While bats are famously able to carry viruses deadly to humans—such as Ebola, Nipah, and coronaviruses related to COVID-19—without showing obvious symptoms, new research shows their resilience has limits. A review of experimental infections suggests that bats, like rodents, can become seriously ill when exposed to certain viruses.
“Bats are often portrayed as special because they don’t get sick from viral infections, but evidence for that claim is sparse,” says biologist Maxwell Farrell of the University of Glasgow. Farrell and colleagues analyzed over 100 studies published between 1936 and 2022, examining more than 5,600 bats and rodents infected with 54 different viruses. Their statistical analysis found no clear difference in disease severity or mortality between bats and rodents.
Some bats do tolerate viruses with which they share a long evolutionary history. For example, Egyptian fruit bats (Rousettus aegyptiacus) can carry Marburg virus in the wild without severe illness. However, other viruses, such as West Nile virus, have proven lethal to some bat species. This suggests that bats’ famed viral tolerance may be limited to pathogens they’ve co-evolved with.
Understanding how bats manage these infections could inspire new antiviral treatments for humans. Farrell notes, “Bat-inspired drugs could be extremely useful for viruses we might be worried about emerging in the future.”
Virologist Arinjay Banerjee of the University of Saskatchewan adds that while bats’ immune systems are fascinating, the idea that they never get sick is a misconception. “Bats can’t tell us when they feel unwell,” he says. Symptoms like fatigue or malaise are difficult to measure in flying mammals, making it challenging to assess illness.
The study has limitations: not all viruses have been tested in bats or other animals, and biosafety concerns restrict experiments with deadly pathogens. Expanding research to more species and viruses could reveal new insights into how animals tolerate infections, potentially informing human medicine.