‘Staggering disease’ discovered in Colorado mountain lion

Researchers have identified a rustrela virus (RusV) variant in a wild mountain lion in Colorado. This marks the first documented case of rustrela virus associated “staggering disease” in North America, according to a study published in the August issue of the journal Emerging Infectious Diseases.

Staggering disease is an often-fatal neurologic condition that has threatened domestic cats in Europe for several decades, primarily in Sweden and Austria. Only recently have scientists linked staggering disease to RusV, a relative of the rubella virus responsible for German measles in people.

According to the journal report, in May 2023, Colorado Parks and Wildlife (CPW) officials in Douglas County euthanized an approximately 1-year-old, free-ranging female mountain that was unable to use its hind legs. Subsequent tissue analysis revealed the presence of RusV.

The lead author on the paper, Dr. Karen Fox, former CPW wildlife pathologist and current veterinary anatomic pathologist at Colorado State University’s Veterinary Diagnostic Laboratories, said in a statement that the diagnosis of staggering disease was challenging, and final confirmation was only possible through collaboration with researchers at the Friedrich-Leoffler-Institut in Germany.

The most common clinical sign of staggering disease is hind-limb ataxia with generally increased muscle tone, which results in a staggering gait. A range of other neurologic signs may occur, including the inability to retract the claws, hyperesthesia, and occasionally tremors and seizures. Behavioral changes include enhanced vocalization, depression, increased affection, and, in rare occasions, aggression.

Staggering disease usually lasts a few days to a few weeks, but may also continue for more than a year, and generally results in deterioration requiring euthanasia for animal welfare reasons.

Scientists don’t yet know how widespread RusV is in either domestic cats or wildlife, said Dr. Fox. In Europe, RusV causes staggering disease in cats, but also has been found in a host of other species, including rodents, a donkey, and marsupials.

Surveillance for RusV in small rodents might identify a local reservoir host because rodents of the genus Apodemus have been identified as likely viral reservoir hosts, the article continued. Although Apodemus mice are not indigenous to North America, several genera of small rodents are found throughout Colorado and could serve as candidates for further screening. In addition, future studies should consider that the zoonotic potential of RusV has not been determined.

“Given the wide host range of the virus in Europe, RusV should be considered as a possible cause for neurologic diseases in all mammal species in North America,” the article’s authors concluded.

A version of this story appears in the October 2024 print issue of JAVMA