The rabbits photographed around Fort Collins, Colorado, in August 2025 were affected by cottontail rabbit papillomavirus, also called Shope papillomavirus. It causes wart-like growths that can look like horns or tentacles, but they are not literal tentacles—and Colorado Parks and Wildlife says the rabbit-specific virus does not cause disease in people, dogs, cats or other species.
What are the horn-like growths on the rabbits?
They are papillomas: growths on the skin caused by cottontail rabbit papillomavirus. Colorado Parks and Wildlife (CPW) says they usually appear as black nodules on a rabbit’s head and can become elongated, giving them a horn-like appearance. The viral images may look like the animals have tentacles, but that description is visual shorthand for the shape of the growths, not what they are.
The sightings that drew widespread attention were reported around Fort Collins in August 2025. The Associated Press described the cause as the “mostly harmless” Shope papillomavirus. The alarming appearance alone does not indicate a new pathogen or a threat to people.
Can the virus infect people, dogs or cats?
No. CPW says the virus is specific to rabbits and does not cause disease in other species; the Associated Press likewise reported that it does not infect humans, dogs or cats. The reports of rabbits with facial growths therefore do not establish a human outbreak risk.
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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesStill, do not handle wild rabbits. Keeping distance protects both people and wildlife, and a wild animal with visible growths should be left to wildlife authorities rather than captured or treated at home.
How does rabbit papillomavirus spread?
Transmission is among rabbits. The Associated Press reports that fleas and ticks can spread the virus and are most active in summer. That helps explain why seasonal contact with biting insects is relevant, but it does not mean every rabbit with a skin growth is infected or that the virus spreads between people and pets.
Outdoor domestic rabbits may be exposed through contact with infected wild rabbits or biting insects. Owners can reduce opportunities for that contact by keeping pet rabbits separated from wild animals and discussing suitable housing and insect precautions with a rabbit-experienced veterinarian.
Do infected rabbits recover?
Most wild cottontails survive, and the growths usually go away after the animal mounts an immune response, according to CPW. In wild rabbits, the main concern is whether the growths interfere with eating or drinking. Growths near the mouth or eyes may also warrant particular concern because location can affect normal function.
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CPW does not recommend euthanizing a wild rabbit with papillomas unless the growths impair eating or drinking. If you see an affected wild rabbit, do not try to remove the growths; contact the appropriate local wildlife agency if the animal appears unable to feed or drink.
What should owners of pet rabbits do?
CPW says disease can be more severe in domestic rabbits and recommends veterinary treatment for affected pets. If a pet rabbit develops unusual nodules or horn-like growths, contact a veterinarian—ideally one experienced with rabbits—rather than assuming the diagnosis from a photograph.
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- Keep the rabbit away from wild rabbits and seek veterinary advice about outdoor exposure and biting insects.
- Do not apply human wart removers, pesticides or antiviral medicines unless a veterinarian directs you to.
- Do not cut, pull or otherwise attempt to remove a growth at home.
Has the virus spread beyond the United States?
The documented Fort Collins incident was in Colorado, and similar-looking rabbits have drawn attention elsewhere in the United States. The official information cited here does not establish an international outbreak or provide an official nationwide case count. Claims that the virus has spread beyond the United States should therefore be treated as unconfirmed, not as evidence of a global emergency.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why is the disease called Shope papillomavirus?
The Associated Press reports that Richard E. Shope, a professor at The Rockefeller University, discovered the disease in cottontails in the 1930s. Reporting has also connected research on the rabbit virus to scientists’ understanding of relationships between viruses and cancer. Those historical connections help explain the name and scientific interest; they are not evidence of a new outbreak.
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