Following the mysterious deaths of three squirrel breeders in Germany, a research team led by Dr. Martin Beer, head of virus diagnostics at the Friedrich-Loeffler Institute, decided to conduct a little investigation. What they stumbled upon was a new bornavirus that was transmitted from squirrels to humans, resulting in three fatal bouts of encephalitis. A statement released by the European Centre for Disease Prevention and Control called the discovery an “emerging threat.”

“This cluster of acute fatal encephalitis in three squirrel breeders possibly related to an infection with a newly identified bornavirus is an unusual event,” the ECDC explained. “The role of new bornavirus in the aetiology of these cases, the identification of natural hosts, reservoirs, and transmission route require additional investigations.”

Findings from the report revealed that three squirrel breeders — all of which were in their 60s and knew each other — had developed encephalitis, an inflammation in the brain, and died between 2011 and 2013. Two of the men had reported suffering scratches and bites as the result of handling exotic squirrels. All three men were hospitalized in intensive care units and treated for initial symptoms of fever, chill, and weakness, and delayed symptoms of confusion and loss of motor function. They eventually went into a coma and died two to four months after the onset of their initial symptoms.

Researchers conducted genetic testing on one of the squirrels owned by one of the breeders and discovered a new type of bornavirus that they dubbed VSBV-1. According to the EDCD, bornaviruses are a group of viruses that generally affect rhesus monkeys, horses, sheep, cattle, goats, rabbits, deer, llamas, alpacas, cats, rats, mice, shrews, gerbils, dogs, and ostriches. Antibodies from this particular bornavirus were found in the blood and spinal fluid of one of the breeders.

“Pending the completion of the cluster investigation, feeding or direct contact with living or dead variegated squirrels should be avoided as a precautionary measure,” the ECDC added. “Further investigations are ongoing to characterize these cases. Testing cases of human encephalitis for this newly identified bornavirus, especially in areas where the presence of bornavirus is documented in animals, can contribute to a better understanding of the risk of bornavirus infection in humans.”

This isn’t the first reported case of a squirrel being blamed for a potentially fatal disease. Back in 2012, officials in Riverside County, Calif., discovered a squirrel at a nearby campground that was infected with the bubonic plague. Rodents, such as squirrels and rats, can contract the plague via a tick or flea infected with the Yersinia pestis bacteria. Thankfully for campers in Southern California, the squirrel was not deemed a risk due to the low levels of the bacteria found in its system.

Source: Ulrich R, Siegel M, Beer M, et al. A Variegated Squirrel Bornavirus Associated with Fatal Human Encephalitis. New England Journal of Medicine. 2015.