Three men who worked as squirrel breeders in Germany died from inflammation of the brain earlier this year. According to the European Centre for Disease Prevention and Control, they “very likely” contracted a newly identified virus from infected squirrels. 

All three of the men who suffered fatal encephalitis were residents of the state of Saxony-Anhalt, and they were between the ages of 62 and 72. They bred variegated squirrels (Sciurus variegatoides), common tree squirrels from Central America that are popular as exotic outside pets. And while they knew each other, the men didn’t live near one another, and it’s unclear if they exchanged animals. They began showing symptoms including fever, shivering, fatigue, weakness, and walking difficulties. The first patient was seen in 2011, and the other two went to different hospitals in 2013. Because of their increasing confusion and psychomotor impairment, they were admitted to neurology wards where they developed problems with eye movement. Their situations worsened, and they died within a few days, even after spending time in intensive care with a mechanical ventilator. 

When a genetic analysis was conducted on tissue from the carcass of a variegated squirrel that belonged to the third patient, researchers found sequences of a newly identified type of bornavirus. First described in the 18th century, Borna disease virus infects many vertebrates, ranging from gerbils to dogs to military horses. And it can result in a fatal neurologic disease. The first evidence of possible human infections with bornaviruses were reported in a 1985 study of patients with major depressive psychiatric disorders. 

Using the same metagenomics approach with the squirrel tissue, researchers found the same gene sequences in the brain samples of the three squirrel breeders. However, a direct causal relationship between the presence of genetic material in the human brain and encephalitis hasn’t been established. 

Furthermore, the transmission route in these three cases hasn’t been determined either. It’s possible they may have become infected through bites or scratches. Although, airborne transmission by inhaling air contaminated by feces or urine can’t be ruled out just yet. Further investigation is needed to figure out the natural hosts and reservoirs of this new bornavirus. While this is being called an “unusual event,” it might be a good idea to avoid direct contact with variegated squirrels, dead or alive, for now.

[H/T Live Science]