Frankenstein rabbits? Veterinarians tell the real story

Sightings of horned rabbits hopping in northern Colorado made national headlines in recent weeks, earning the bizarre-looking animals nicknames such as "Frankenstein bunnies," "zombie rabbits," and "demon rabbits."

While the images are indeed unusual, veterinarians familiar with rabbit health stress that these cases are not evidence of the fabled jackalope or an exotic disease, but rather of Shope papillomavirus (SPV), a well-known viral infection first described nearly a century ago.

"The only thing new about SPV is the recent hype on social media," said Dr. Bill Guerrera, co-owner of Colorado Exotic Animal Hospital.

Wild vs pet rabbits

Known also as Cottontail Rabbit papillomavirus, SPV is a DNA virus transmitted primarily by mosquitoes, ticks, and fleas. It is endemic in cottontail rabbits, especially in the Midwest, and tends to appear more often during warmer months when insect activity peaks.

The virus causes wart-like tumors that may keratinize into hard, black, horn-like projections. These growths typically appear on the rabbit's head, ears, and eyelids, sometimes impairing vision or feeding. In most wild rabbits, the immune system eventually resolves the infection and the growths regress.

"Wild rabbits develop the characteristic benign growths, but these regress after several months, and the rabbit goes on its happy way," Dr. Guerrera explained. "Problems can arise when the growths interfere with eating or vision but otherwise are fairly harmless."

While SPV is rarely diagnosed in domestic rabbits, when it is, it can be serious, as the papillomas are more likely to become malignant.

"Based mostly on experimental work, we know that malignant transformation happens in about 75% of infected domestic rabbits, compared to only around 5% of infected cottontails," explained Dr. Javier Asín Ros, associate professor and diagnostic veterinary pathologist at the California Animal Health and Food Safety Laboratory at the University of California-Davis School of Veterinary Medicine.

In more than 25 years of practice, Dr. Guerrera has only seen one suspected case of SPV in a domestic rabbit, and that was more than 15 years ago.

"It's rare in pets, but veterinarians should be aware of the potential," he said.

Little Bigfoot?

The recent wave of attention began around mid-August, when residents of Fort Collins, Colorado, shared photos and videos of rabbits with protrusions on TikTok and X. Within days of posting, local, national, and international media were jumped on the story.

Colorado Parks and Wildlife confirmed the SPV diagnosis and emphasized that the virus poses minimal risk to humans, pets, or other wildlife species. The agency reported a surge in calls from concerned residents after the images circulated.

"We need to be clear that SPV poses no threat to humans or to animals different to rabbits," Dr. Ros said. "Even though in some wild rabbits the lesions may look very bizarre, we should insist that it is a benign disease and that complications are rare."

Dr. Guerrera recommends pet owners keep their rabbits away from cottontails, which may be infectious, and to stay up to date on the rabbit hemorrhagic disease vaccine, a virus that poses a far greater risk to rabbits.

The "horned rabbit" may look unsettling, but for veterinarians, the story serves as a reminder of a long-known virus with occasional clinical significance. The folklore of jackalopes may have found a modern echo on social media, but the reality is simpler: SPV is a seasonal, insect-borne infection that most wild rabbits survive and that domestic rabbit clinicians should keep on their radar.

Dr. Ros sees the event as an opportunity. "It can foster interest in this viral disease and perhaps encourage surveys in different states to see what wild rabbit species are affected and what factors influence malignant transformation," he said. "It's also a good opportunity to remind people not to touch wild rabbits and to keep their pets protected."