November 5, 2025 – When a young mountain lion in Colorado began stumbling and trembling last year, wildlife officials knew something was seriously wrong. The 1–year–old cat couldn’t steady her back legs and fell repeatedly when she tried to walk. After humane euthanasia, testing revealed an alarming discovery – she was the first confirmed case of “staggering disease” ever reported outside of Europe.
For more than 50 years, staggering disease has been known to affect domestic cats overseas. Cats with the disease often struggle to walk, lose coordination, and may become unable to stand. The illness is caused by a virus just identified in 2022, and there’s no known cure or treatment. Infected cats typically die or must be humanely euthanized to prevent suffering.
Until the case in Colorado, the disease had never been documented in North America. Its sudden appearance raised critical questions. How did the virus reach the United States? Could it spread to domestic cats? And what role might wild rodents play in its transmission?
THE STUDY
Dr. Karen Fox and her team at Colorado State University are leading a new Foundation–funded study to find answers. The team will conduct nationwide surveillance to determine how widespread staggering disease might be in U.S. wildlife and domestic cats.
Researchers will identify and test suspected cases using advanced diagnostic techniques, while also studying small rodents to see whether they serve as reservoir hosts for the virus – a pattern already observed in Europe.
WHY IT MATTERS
This work will help veterinarians, wildlife biologists, and pet owners understand whether staggering disease poses a threat to cats in the United States. By mapping where the virus exists and how it spreads, Dr. Fox’s team aims to provide early warning signs that can guide both wildlife management and veterinary care.
“When I saw a video of this mountain lion with a wobbling back end my first thought was that it had probably been hit by a car,” said Dr. Fox. “It was only at the urging of wildlife managers who felt something was off about the animal that we conducted a full necropsy investigation and discovered this surprising occurrence of staggering disease. We thought, ‘How often are cats, especially outdoor cats, euthanized with sudden hind leg paresis that is presumed to be due to trauma? How often might these be unrecognized cases of staggering disease? With help from pet owners and veterinarians, and funding from Morris Animal Foundation, we can conduct necropsies on cats that have been euthanized after showing signs of staggering disease. But we need help to identify suspect cases and get them into the lab for testing’”.
Understanding emerging diseases like this one is vital to protecting animals everywhere — from wild mountain lions to the pets we call family. When wildlife falls ill, it can be a warning about the health of the environment we all share. Protecting them means protecting the animals — and people — closest to us.
SUPPORT GROUNDBREAKING RESEARCH
Research like this is changing what’s possible for animals. Make a gift today to support studies that protect the pets and wildlife we love — in your community and around the world. Together, we can build a healthier future for all animals.
LEARN MORE AND HELP ADVANCE UNDERSTANDING OF STAGGERING DISEASE
Dr. Karen Fox and her team at Colorado State University are seeking additional case submissions to better understand how this deadly virus affects cats in the United States.
If you are a veterinarian, wildlife professional, or pet owner who has encountered cats showing neurological signs such as ataxia, staggering gait, limb weakness, or difficulty jumping, you can help by submitting cases to the ongoing Rustrela virus (RusV) study.
Qualifying cases receive free necropsy and histopathology testing.
Learn more or submit a case here.
By sharing information or suspected cases, you’re helping scientists uncover answers that could save feline lives — and protect the health of animals everywhere.
