When Colorado Parks and Wildlife euthanized a mountain lion in Douglas County last year, there was little explanation for what could have led the predator to become hobbled and disoriented, barely able to move.

A video captured by a homeowner on May 12, 2023, showed the mountain lion dragging itself across the ground using its front paws, struggling to rise as it staggered forward. A postmortem investigation of the mountain lion reportedly found no skeletal abnormalities that could explain its lameness.

Now, just over a year after the 1-year-old female lion was reported to Colorado Parks and Wildlife, scientists say they have discovered the cause of her ailment: staggering disease, a usually fatal neurological syndrome found in domestic cats in Europe.

It is the first time scientists have found the rustrela virus, which was recently identified as the cause of staggering disease, in a mountain lion in North America, according to a study published this week in the journal “Emerging Infectious Diseases.”

The lead author of the paper Dr. Karen Fox said in a news release that the diagnosis of staggering disease was a challenge, and final confirmation was only possible through collaboration with researchers at the Friedrich-Loeffler-Institut in Germany.

Fox, a research scientist with Colorado State University’s College of Veterinary Medicine and Biomedical Sciences in Fort Collins, was also previously a pathologist with Colorado Parks and Wildlife.

Scientists don’t yet know how widespread the virus is in either domestic cats or wildlife populations in Colorado. In Europe, rustrela virus causes staggering disease in cats but has also reportedly been found in a wide range of other species, including rodents, a donkey and marsupials.

The “remarkably broad range” of other mammals that can be hosts of the rustrela virus, or RusV, raises concern that the virus could be spread between people and animals, though that has not yet been researched, according to the study.

“Given the wide host range of the virus in Europe, RusV should be considered a possible cause for neurological diseases in all mammal species in North America,” the study states.

The study suggests studying small rodents in Colorado should be explored to determine whether such rodents could be reservoir hosts, or carriers of the virus that don’t experience any negative effects.

Veterinarians at Colorado State University and Colorado Parks and Wildlife will also be looking carefully for new cases, according to a news release from the agency. If members of the public observe mountain lions that are staggering, having trouble walking or behaving abnormally, they should contact their local Colorado Parks and Wildlife office to report the behavior, the release states.

“Now that we know what we’re looking for, it should be easier to find new cases if they are out there,” Fox said in a statement. “With continued collaboration, we plan to learn what we can from our colleagues in Europe while we continue to look for new cases of staggering disease here in Colorado.”