A brand new study out this week in the Emerging Infectious Diseases journal has revealed that the rustrela virus—most commonly known for the "staggering disease" it causes—has been found for the first time in a North American mountain lion. In May 2023, the mountain lion was found by a homeowner in Douglas County, Colo., sheltering between her basement window well and a nearby spruce tree. Confused by the behavior of the generally aloof animal, the homeowner filmed it dragging itself forward with its front paws, unable to stand or use its hind legs. After Colorado Parks and Wildlife (CPW) officers tranquilized then euthanized the animal (with a shot to the chest to protect the brain for a necropsy), a tissue analysis unveiled the presence of rustrela virus, which causes the fatal "staggering" symptoms in domestic cats.
Diagnosis of the condition was challenging according to CPW wildlife pathologist, Dr. Karen Fox, particularly considering the unprecedented nature of such a discovery in an American lion. Due to these complex conditions, final collaboration and confirmation was provided by researchers at the Friedrich-Leoffler-Institut in Germany. In Europe, there are considerably more instances of the rustrela virus, with it causing staggering disease not just in cats, but in a wide variety of other animals such as rodents, marsupials and even a donkey. Despite this, the connection between the virus and the disease was only discovered "recently," according to Fox.
Dr. Fox, who also serves as a research scientist at Colorado State University Fort Collins (CSU), emphasized it is not currently known how widespread the neurological disease is, either in domestic cats or the wildlife population. “Now that we know what we’re looking for, it should be easier to find new cases if they are out there,” Fox said. “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.”
Any Coloradans, or visitors to the state, who observe mountain lions that are staggering, having trouble walking or behaving abnormally, should contact the local Colorado Parks and Wildlife office to speak with a wildlife officer and report the behavior.
