Are there Frankenstein rabbits in Colorado?

People in Fort Collins, Colorado recently reported seeing what seem to be horned rabbits in recent weeks, resulting in these animals getting the nicknames “Frankenstein bunnies,” “zombie rabbits,” and “demon rabbits.”

Wild rabbits in Fort Collins, Colorado, have gained traction on social media as well as news outlets all over the world for their wart-like tumors that look like horn projections (Image courtesy of the American Veterinary Medical Association)

However, according to American Veterinary Medical Association (AVMA), these ‘demon rabbits’ actually have Shope papillomavirus (SPV), a well-known viral infection which was first described almost a century ago.¹ The virus is an endemic in cottontail rabbits and is transmitted primarily by fleas, mosquitoes, and ticks. It tends to appear in rabbits more often during warmer months when insect activity peaks.¹

SPV causes wart-like tumors that could keratinize into dark, hard, horn-like projections that grow on the rabbit’s head, ears, and eyelids, which can sometimes impair their vision or feeding. For most wild rabbits, their immune system resolves the infection and the growths regress eventually. This viral infection is rarely diagnosed in domestic rabbits, but it is serious when it is because the papillomas are more likely to become malignant. For domestic rabbits, if left untreated, it can progress to malignant cancer.

If a domestic rabbit is presenting with signs of SPV, veterinarians need to surgically or manually remove the nodules and send them to a pathologist for evaluation via histopathology. This will help the veterinary team determine the cause of the papillomas, whether they are benign or malignant, and if they have transformed to squamous cell carcinomas. These nodules occasionally go away on their own, but surgical removal is recommended because they can become malignant and can potentially metastasize to lymph nodes and lungs.²

"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," Javier Asin Ros, DVM, PhD, DECVP, 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, explained to the AVMA.¹

Although rare in domestic pets, veterinary professionals believe this is still something veterinarians should know its potential risks.

This recent wave of attention to SPV is due to residents in Fort Collins sharing photos and videos on social media of the rabbits with protrusions, gaining local, national, and international media attention within days of posting. The Colorado Parks and Wildlife confirmed the SPV diagnosis and emphasized that it poses a minimal risk to pets, humans, or other wildlife species. Veterinary professionals should recommend to pet owners to keep their rabbits away from cotton tails and to keep them up to date on their rabbit hemorrhagic disease vaccine.

Although unsettling to see these rabbits with SPV, veterinary professionals can see this story as a reminder of a long-known virus with occasional clinical significance, according to the AVMA.

"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," Ros said. "It’s also a good opportunity to remind people not to touch wild rabbits and to keep their pets protected," he concluded.¹

References

1. Nolen RS. Frankenstein rabbits? Veterinarians tell the real story. American Veterinary Medical Association. Published September 4, 2025. Accessed September 22, 2025. https://www.avma.org/news/frankenstein-rabbits-veterinarians-tell-real-story
2. PetMD Editorial. Shope Papilloma Virus in Rabbits: What It Is and How To Keep Your Bunny Safe. Petmd.com. Published October 2008. Accessed September 22, 2025. https://www.petmd.com/rabbit/conditions/viral/c_rb_shope_papilloma_virus