A mysterious virus may have jumped from squirrels to humans, and caused the death of three German squirrel breeders, Rachael Rettner reports for Live Science.

In a recent paper in the New England Journal of Medicine, researchers described the details of a cluster of odd cases of encephalitis or brain inflammation in Saxony-Anhault, Germany. Between 2011 and 2013, three men developed acute encephalitis. Their symptoms included fever, fatigue, muscle spasms, confusion, and vision problems. Each went into a coma and died within a span of two to four months.

When the usual encephalitis suspects didn’t turn up in tests, researchers dug deeper, writes Rettner. They found traces DNA from a virus they had never before encountered in the patients’ brain tissue. Further tests revealed, that this particular pathogen, nicknamed VSBV- 1, came from the borna virus family, a group of viruses commonly found in horses, cattle, birds and other animals. Researchers already knew that borna viruses could jump between species — in the 1990s, borna viruses were loosely linked to some human psychiatric disorders, but there’s some debate as to whether it actually causes diseases in humans.

Though they lived in different places, all three men had one thing in common: they all bred exotic variegated squirrels (Sciurus variegatoides) from Latin America. Occasionally, they got together to swap tips and breeding pairs, the researchers explain in NEJM. Raising these animals comes with an occasional scratch or bite — an easy way for a virus to pass from an animal to a human. Sure enough, one of the squirrels tested positive for the virus.

At this point, it’s still impossible to say conclusively that this specific virus caused the brain inflammation that these three men experience, but a case report released by the European Center for Disease Control and Prevention argues that the evidence against the virus is pretty damning.

Despite the evidence, it’s a bit early to panic, notes HealthDay News. Researchers still have a lot to learn about the virus, from how it might transmit to where the squirrels themselves might have contracted it. At this point, there’s no evidence that it can spread to other squirrel species or from human to human. Still, perhaps resist the urge to feed squirrels at your local park, despite how cute they might be. That's better for the squirrels anyway.