First case of 'staggering disease' in North America found in a Colorado mountain lion

A mountain lion euthanized in Colorado last year had the first recorded case of “staggering disease” in the species in North America, Colorado Parks and Wildlife announced Tuesday.

CPW officers were forced to euthanize the sick cat in May 2023 because it was unable to use its hind legs. An analysis of the mountain lion's tissues revealed the presence of the rustrela virus, or RusV.

The Centers for Disease Control and Prevention released an early study on the virus , with a final version coming in August in its monthly "Emerging Infectious Diseases" report .

The early report contained more details about the animal and virus: On May 12, 2023, CPW received a report about a 1-year-old female mountain lion in a residential area of Douglas County with "severe hind leg ataxia and paresis."

"The animal was reluctant to rise and had markedly decreased capacity to move or bear weight on the hind end," the study reads. "The animal moved by pulling itself forward with the front legs, while minimally propelling itself forward with the hind legs. The animal appeared depressed but was still responsive to stimuli."

The CDC study reads that wildlife officers tranquilized the animal, euthanized it and conducted an investigation to determine why it appeared so sickly.

The mountain lion's "histopathology, and metatranscriptome sequencing suggested staggering disease," so tissue samples and sequence data were sent to the Friedrich-Loeffler-Institut in Germany .

"We found particularly abundant or large, dot-like signals in the granule cell layer of the hippocampus and in Purkinje cells of the cerebellum, similar to findings from staggering disease cases in cats from Europe," the study reads.

Staggering disease has been documented in domestic cats in Europe, particularly Sweden and Austria, since the 1970s. In Germany, it was detected in some zoo animals, including lions, the study reported.

In the study's conclusion, researchers wrote that the "results demonstrate the presence of a RusV variant in North America that is divergent from those previously described from Europe. The clinical signs, histologic lesions, and infected target cells observed for the wild mountain lion in Colorado, USA, meet the case definition for staggering disease."

The CDC study noted that a deeper investigation is needed to confirm if staggering disease is affecting other mountain lions in the Colorado population.

Small rodents in the genus Apodemus may host the virus as well. While those specific rodents are not indigenous to North America, several rodent genera are found in Colorado and might need to be screened for the virus, the study reads.

"Of note, a remarkably broad range of other mammalian RusV hosts have been identified in Germany, including equids, mustelids, rodents, and marsupials, raising concerns about a zoonotic potential of RusV," the study concluded. "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 study's lead author, Dr. Karen Fox with Colorado State University College of Veterinary Medicine and Biomedical Sciences, said now that wildlife officials know what to look for, it should be easier to find any new cases.

"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," Dr. Fox said.

This story was first published by Robert Garrison and Stephanie Butzer at Scripps News Denver .