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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallA fatal neurologic illness in a young mountain lion in Douglas County, Colorado, was linked to a North American variant of rustrela virus (RusV), a virus previously documented mainly in Europe. The 2024 report is the first published RusV case in a wild mountain lion in North America. It is one confirmed animal, not evidence that the virus is widespread in Colorado, newly arrived, or known to infect people.
What happened to the Colorado mountain lion?
Colorado Parks and Wildlife received a report on May 12, 2023, about an approximately one-year-old free-ranging female mountain lion in a residential area of Douglas County. She had severe hind-leg ataxia and paresis, was reluctant to rise, and had greatly reduced ability to move or bear weight on her hindquarters.
Wildlife officers tranquilized the lion and euthanized her with a gunshot to the chest so neurologic tissues could be preserved for examination. The animal’s clinical deterioration was fatal.
How researchers identified rustrela virus
The investigation combined necropsy, histopathology, immunohistochemistry, molecular testing, and metatranscriptome sequencing.
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Other causes tested negative
Initial central-nervous-system testing did not detect several possible causes of encephalitis, including rabies, canine distemper virus, West Nile virus, feline panleukopenia virus, influenza A, Toxoplasma gondii, or feline infectious peritonitis virus.
RusV was found in nervous tissue
Sequencing pooled brain and spinal-cord material produced a genome sequence matching rustrela virus reference strains. Follow-up tests detected RusV RNA in those tissues. In situ hybridization localized viral RNA inside neurons in multiple brain regions and through nearly all levels of the spinal cord.
The researchers described severe nonsuppurative meningoencephalomyelitis and neuronal damage. The neurologic signs and microscopic lesions resembled staggering disease previously reported in cats. They concluded that the case met the study’s definition of staggering disease and that RusV’s causal role was likely.
What “first U.S. case” means—and does not mean
| Established by the report | Not established by the report |
|---|---|
| A RusV variant was identified in one wild mountain lion in Colorado. | How common RusV is in Colorado or elsewhere in North America. |
| Viral RNA was demonstrated in the animal’s brain and spinal cord, including infected neurons. | Whether RusV is established or spreading in the region. |
| The animal’s signs and lesions fit staggering disease; the authors considered causation likely. | A transmission route, reservoir host, or infection rate in rodents or other wildlife. |
| This is the first published North American RusV variant reported from a wild mountain lion. | That people are infected or face a demonstrated risk from this case. |
The study itself says more investigation is needed to determine whether RusV is enzootic in the region. A single case cannot provide a prevalence estimate or describe the virus’s usual effects in mountain lions.
How closely was the Colorado virus related to European viruses?
The paper reports sequence comparisons, not percentages of infected animals or measures of human risk:
- The Colorado sequence had 69.9% mean nucleotide identity with German sequences.
- It had 68.9% mean nucleotide identity with sequences from Austria and Sweden.
- European sequences compared with one another showed 76.7% nucleotide identity.
- Mean amino-acid identity between the Colorado sequence and European sequences was 75.6%–78.1% for the nonstructural and structural polyproteins.
These figures describe genetic similarity in the analyzed sequences. They do not show transmission frequency, geographic spread, or the probability of human infection.
Can rustrela virus infect people?
The zoonotic potential of RusV has not been determined. This mountain-lion report does not demonstrate human infection or establish a human health risk. The virus has been detected in multiple mammalian hosts in Europe, which is why the authors recommend considering RusV when investigating unexplained neurologic disease in North American mammals; that recommendation is a reason for surveillance, not proof of spread among North American species.
Possible next steps proposed by the authors include retrospective RusV testing of North American feline encephalitis cases with no identified cause and surveillance of small rodents. Those proposals do not establish that local rodents transmit the virus.
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What should you do if you see a sick or dead mountain lion?
- Do not approach, touch, feed, or attempt to move the animal.
- Keep children and pets away from it.
- Contact the nearest Colorado Parks and Wildlife office to report a sick, injured, or deceased wild animal.
- If you encounter a live mountain lion, remain calm, do not run, and give it an escape route. After an encounter or attack, contact authorities and follow their instructions.
These are Colorado Parks and Wildlife’s general wildlife-safety recommendations; they are not special handling rules created for RusV.
Why this case matters to wildlife surveillance
The finding expands the known geographic and host context for rustrela virus and shows why unexplained encephalitis in wildlife may require specialized molecular testing. It also gives investigators a concrete target for reviewing archived feline neurologic cases and surveying potential wildlife hosts.
At the same time, the study’s authors emphasize the central limitation: “This report is limited to a single case of staggering disease in Colorado.” Their broader conclusion is that, “Considering its wide host range in Europe, rustrela virus should be considered as a cause for neurologic diseases among mammal species in North America.” Those statements support further investigation, not a claim that Colorado’s mountain lions are experiencing an outbreak.
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