New findings on the origins of hepatitis A virus (HAV) are now suggesting that bats may have played a critical role in the evolution of modern liver disease, Gizmodo reports.

In a recent study, German scientists at the University of Bonn analyzed the genes of more than 203 unique animal species and found that 13 different types of bats, rodents, hedgehogs and shrews carried some form of hepatovirus similar to HAV in their DNA.

Now researchers theorize that hep A probably originated in an insect and then jumped to the small mammals, particularly bats, that fed on it; the mammals left the virus behind their droppings, and from there it eventually infected the human population.

The latest research contradicts previous scientific theories about HAV origins, which suggested that the virus never had a non-human vector.

In fact, scientists now guess that long before hep A affected humans, the virus was probably kept alive by bats (who now no longer carry HAV) until the population grew large enough for sustained human-to-human transmission.