At least three German citizens have died from complications related to a virus spread by a rare species of squirrel. According to a report from Live Science, the victims, who were all professional squirrel handlers, contracted the virus after coming into contact with variegated squirrels carrying the disease. Now, a new study shows how the virus managed to spread from the animals to their handlers.

The variegated squirrel, a rare tree squirrel from Southern Mexico and Central America, has shown that it has the potential to transmit the virus to humans. Scientists aren’t positive how the captive animals contracted the variegated squirrel 1 bornavirus (VSBV-1). They are still trying to determine if the virus originated in Central America or was contracted at a later time.

According to Martin Beer, the head of virus diagnostics at the Friedrich-Loeffler Institute in Insel Riems, Germany, VSBV-1 can be easily transmitted to humans handling squirrels that are infected. The victims each developed a condition called encephalitis, or massive swelling in the brain. They died between two and four months after coming into contracting the virus.

One of the men was bitten, while the other two were scratched by the squirrels. They all died from complications related to the virus between 2011 and 2013. Each of the victims was over the age of 60, and was experiencing other health conditions that likely made them more susceptible to the virus.

Bornaviruses usually infect animals such as birds, horses, and sheep, and scientists have been unsure if they could be passed along to humans. Other symptoms of the virus include chills, weakness, fever, difficulty walking, and confusion.

Scientists believe that this version of the virus is only found in variegated squirrels, and cannot be transmitted between humans. They warn against handling any variegated squirrels that might be infected, dead or alive.