The black, horn-like growths reported on rabbits around Fort Collins in August 2025 were associated with cottontail rabbit papillomavirus, a virus specific to rabbits. The growths are not actual horns; most infected wild cottontails survive and the growths go away, but lesions that interfere with eating or drinking are a welfare concern.
Do not approach or handle a sick or injured wild rabbit, and keep pets away. Observe it from a distance; contact a local Colorado Parks and Wildlife (CPW) office if help is needed. For a domestic rabbit that may have been exposed or has lesions, contact a veterinarian.
The short answer
- What happened: Residents reported rabbits with horn-like growths around Fort Collins in August 2025.
- What caused the appearance: The growths were associated with cottontail rabbit papillomavirus, also called rabbit papillomavirus in CPW guidance.
- What the growths are: Black skin nodules that can become elongated and look like horns—not actual horns.
- Risk to other species: CPW says the virus is specific to rabbits and does not cause disease in other species.
- What to do: Keep your distance and keep pets away. Contact CPW if a wild rabbit needs help; consult a veterinarian about a domestic rabbit.
Where and when were the rabbits seen?
The reports that drew attention to the “Frankenstein bunny” story came from around Fort Collins in August 2025. The Associated Press reported on August 13 that residents had spotted rabbits with horn-like growths and contacted CPW. That reporting documents a local episode; it does not establish how many individual rabbits were affected or show that there is a current outbreak.
CPW’s species guidance describes rabbit papillomas as a known condition. The reports should be understood as sightings of rabbits with unusual growths, not evidence of a new statewide surge. The Associated Press report describes the 2025 episode.
What were the black “horns”?
CPW describes black skin nodules, usually on the head, that can become elongated enough to look like horns. They are papilloma growths associated with a rabbit-specific virus—not actual horns or antlers.
A Fort Collins-area resident quoted by CBS News Colorado described seeing “black quills or black toothpicks sticking out all around his or her mouth.” That is a witness’s description, not a scientific diagnosis. A photograph alone cannot establish the cause of an individual rabbit’s growths. CBS News Colorado reported on the sightings.
What is the virus called?
CPW calls the cause cottontail rabbit papillomavirus. It is also commonly called rabbit papillomavirus or Shope papillomavirus. The Associated Press used the name Shope papillomavirus in its report about the Fort Collins sightings.
The virus was first identified in 1933. The Denver Museum of Nature & Science explains that its study helped scientists investigate the relationship between viruses and cancer. That research history does not mean the rabbit virus is the same as human papillomavirus. The Denver Museum of Nature & Science provides historical context.
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Is this the rabbit equivalent of human HPV?
It is a rabbit-specific papillomavirus, not human HPV. CPW states that the virus is specific to rabbits and does not cause disease in other species. The historical connection to research on viruses and cancer does not mean the virus infects people or that every rabbit with visible growths has cancer.
Are the “mouth tentacles” growing inside the rabbit’s mouth?
“Mouth tentacles” is a vivid description, not a precise diagnosis. CPW describes black skin nodules that may become elongated, and some residents reported seeing growths around rabbits’ mouths. Growths near the mouth can matter if they interfere with eating or drinking.
Do not try to diagnose a rabbit from a photograph. If a wild rabbit appears unable to eat or drink, observe it from a distance and contact a local CPW office for guidance.
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How does cottontail papillomavirus spread?
The supplied official guidance confirms that the virus is rabbit-specific and notes a risk to domestic rabbits, especially where outdoor housing permits contact with wild rabbits or biting insects. The sources reviewed for this article do not establish a detailed transmission route or show that insect activity caused the Fort Collins sightings.
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Can the virus infect people, dogs, or cats?
People
CPW says the virus is specific to rabbits and does not cause disease in other species. Still, avoid handling wild animals. If you have contact with a wild animal, CPW advises contacting a medical doctor or local public health department.
Dogs and cats
CPW’s guidance says the virus does not cause disease in other species. Keep pets away from sick, injured, or dead wildlife as a general precaution.
Domestic rabbits
Domestic rabbits may be at risk, particularly where outdoor housing permits contact with wild rabbits or biting insects. CPW says the disease is more severe in domestic rabbits and should be treated by a veterinarian.
The practical rule is: do not panic, but do not handle wildlife. If a pet has contact with a wild animal, CPW advises contacting a veterinarian.
Is the condition dangerous to the rabbit?
CPW says most infected cottontails can survive the viral infection, after which the growths go away. The growths are a welfare concern when they interfere with eating or drinking. CPW does not recommend euthanizing wild rabbits with papillomas unless the growths interfere with those functions.
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Do not assume that every unusual growth has the same cause. If a rabbit appears sick or injured, avoid handling it and contact a local CPW office for guidance.
What should you do if you see one?
| What you observe | What to do |
|---|---|
| A wild rabbit with growths that appears to be functioning normally. | Observe from a distance, keep pets away, and leave it alone. |
| A wild rabbit that appears unable to eat or drink, or is sick or injured. | Do not approach or handle it. Contact a local CPW office for guidance. |
| A domestic rabbit that may have been exposed or has lesions. | Contact a veterinarian. |
| You or a pet had contact with a wild animal. | Contact a medical doctor or local public health department for human exposure, or a veterinarian for pet exposure, following CPW guidance. |
Do not catch, medicate, feed, or relocate a wild rabbit. See CPW’s wildlife disease-exposure guidance.
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For a domestic rabbit that may have been exposed to wild rabbits or has possible lesions, contact a veterinarian. CPW says the disease can be more severe in domestic rabbits and should be treated by a veterinarian.
CPW notes that outdoor housing can permit contact with wild rabbits or biting insects. Ask your veterinarian about appropriate care and housing for your rabbit.
Why did it seem as if there were so many?
The available reporting describes sightings and calls, not a measured count of affected rabbits. A striking story can attract attention, but the reports do not establish how many individual rabbits were involved or whether the same animals were seen more than once.
There is no verified case total in the sources reviewed for this article. Treat the Fort Collins reports as a dated local event, not evidence of a current statewide outbreak.
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Not every sick rabbit has papillomavirus
Black, horn-like growths were associated with papillomavirus in the Fort Collins reporting, but an unusual appearance alone cannot confirm the cause in an individual animal. Avoid handling sick or injured wildlife and contact CPW if help is needed. For a domestic rabbit, consult a veterinarian.
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Could these growths explain the jackalope?
The horn-like appearance of papilloma growths resembles the antlers shown on the jackalope, a North American folklore creature. The Denver Museum of Nature & Science discusses the horned rabbit in its collection and the history of research into the virus. The resemblance is historical context, not evidence that the jackalope is a biological species.
What the evidence does—and does not—show
The available evidence supports these conclusions:
- Residents reported rabbits with horn-like growths around Fort Collins in August 2025.
- CPW describes cottontail rabbit papillomavirus as specific to rabbits and says it does not cause disease in other species.
- The growths are black skin nodules that can become elongated and horn-like.
- Most infected cottontails can survive, and the growths go away, according to CPW.
- Growths that interfere with eating or drinking are a welfare concern.
- Domestic rabbits may be at risk, and CPW says the disease is more severe in them and should be treated by a veterinarian.
- The reporting does not establish a case count or a current outbreak.
Leave a normally functioning wild rabbit alone, keep pets away from wildlife, and contact CPW if a wild animal appears to need help. Contact a veterinarian about a domestic rabbit that may have been exposed or has lesions.
Sources and further reading
Colorado wildlife guidance: Colorado Parks and Wildlife’s cottontail rabbit page and wildlife disease-exposure guidance.
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FAQ
What are the black horns on the rabbits in Fort Collins?
They are black skin nodules associated with cottontail rabbit papillomavirus. CPW says they can become elongated and look like horns; they are not actual horns.
Can the rabbit virus spread to people or pets?
CPW says the virus is specific to rabbits and does not cause disease in other species. Avoid wildlife contact as a general precaution. If you or a pet has contact with a wild animal, follow CPW’s guidance and contact a medical professional or veterinarian as appropriate.
Should I rescue a wild rabbit whose growths interfere with eating?
Do not try to catch or handle it. Contact a local CPW office for guidance. CPW identifies growths that interfere with eating or drinking as a concern.
Can a domestic rabbit get this disease?
CPW notes that domestic rabbits may be at risk, especially where outdoor housing permits contact with wild rabbits or biting insects. Contact a veterinarian if your rabbit may have been exposed or has lesions.
The Bottom Line
The Fort Collins reports in August 2025 involved rabbits with black, horn-like skin growths associated with a rabbit-specific papillomavirus. CPW says most infected wild cottontails survive and the growths go away, though lesions that interfere with eating or drinking are a concern. Leave wild rabbits alone, keep pets away, and contact CPW or a veterinarian as appropriate.
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