Three squirrel breeders in Germany are dead, apparently from a virus that was able to jump from squirrels to them, and it’s a finding that’s causing some concern among health officials.

The men died between 2011 and 2013, and all of them appeared to have contracted bornavirus, which is usually found in horses, birds, sheep, and rodents. It has the potential to spread, but scientists haven’t yet found evidence it spreads from human to human, according to a UPI report.

All three died just two to four months after getting early symptoms of encephalitis, which include weakness, confusion, chills, and fever. These come about due to swelling in the brain caused by the virus. Testing didn’t indicate why their brains were swelling, however.

Authorities now believe that at least two of them had been bitten or scratched by squirrels, and not by just any type, but by a breed that is native to the tropics of Central America.

A potential link was made earlier this year, prompting the European Center for Disease Prevention and Control to warn people not to come in close contact with squirrels back in February.

However, scientists believe that the threat to other people is fairly low, as scientists have yet to find indications that it spreads to other human sor animals. And it’s not immediately clear why these men got the disease at all.

If it can spread between squirrels and occasionally to humans, it wouldn’t be something that would happen every often and therefore would not risk causing an epidemic.