The idea of a rabbit sprouting horns seems like a creature from a fairy tale, yet photographs and taxidermy mounts of such animals have persisted for decades. While the notion of a true, bone-based horn on a rabbit is a biological impossibility, a scientific explanation exists for the unsettling growths that occasionally appear on their heads. These protrusions are not horns in the traditional sense, but the result of a viral infection that causes physical tumors to form, creating a bizarre and horned appearance. The biological reality behind the myth is far more complex than a simple mutation.
The Legend of the Jackalope
The popular cultural context for the horned rabbit is the American folklore surrounding the Jackalope, a mythical creature described as a jackrabbit with the antlers of an antelope. This legend was popularized in the 1930s by Douglas Herrick and his brother, taxidermists in Douglas, Wyoming. The Herrick brothers famously took a jackrabbit carcass and grafted deer antlers onto its head, creating the first well-known jackalope trophy. This creation was sold to a local hotel and quickly became a tourist attraction. Though purely a product of taxidermy, the Jackalope legend may have been influenced by earlier sightings of real rabbits with unusual growths.
The Scientific Reality Behind the Growths
The growths that sometimes appear on wild rabbits are caused by an infection with the cottontail rabbit papillomavirus (CRPV), also known as Shope papillomavirus. This DNA virus causes the growth of keratinous tumors called papillomas, or warts, on the animal’s skin. The virus was first investigated and identified in 1933 by the American cancer researcher Dr. Richard E. Shope.
Dr. Shope’s discovery established the first mammalian model of cancer caused by a virus. The resulting lesions are not composed of bone like true horns or antlers. Instead, they consist of densely packed keratin, the same protein that makes up a rabbit’s claws and hair. These keratinized masses typically develop on the rabbit’s face, eyelids, and neck, sometimes growing into large, dark, and rough projections. The distinct appearance of these black, horn-like protrusions likely gave rise to some of the earlier tales of horned hares.
How the Growths Affect the Rabbit
The physical manifestation of the infection varies greatly among affected rabbits, ranging from small, isolated warts to extensive, branching growths that genuinely resemble antlers. While many small papillomas are benign and may regress on their own, the larger tumors pose a serious threat to the rabbit’s well-being. Tumors that grow around the mouth can severely impair the rabbit’s ability to forage and consume food, leading to malnutrition and starvation.
Growths near the eyes can block the animal’s vision, making it more vulnerable to predators or accidental injury. In approximately 25% of cases in wild cottontails, the benign papillomas can progress into malignant squamous cell carcinomas, which can metastasize to other organs. The severity of the disease depends on the tumor’s size and location, as well as the rabbit’s overall health and immune response. Young cottontails are particularly susceptible to severe, rapidly progressing infections.
Transmission and Prevalence of the Virus
The Shope papillomavirus is primarily an enzootic disease of the wild eastern cottontail rabbit, but it can also infect other lagomorphs, including jackrabbits and domestic rabbits. Transmission of the virus occurs when a biting arthropod, such as a mosquito or a tick, feeds on an infected animal and then transfers the virus to a new host. The virus is also spread through contact with infected skin cells, often through scratches or abrasions.
Outbreaks are most frequently observed in the Midwestern United States, particularly during the summer and fall seasons when populations of the insect vectors are highest. The virus is highly species-specific, meaning it generally only infects certain types of rabbits and hares. Crucially, the Shope papillomavirus does not pose a direct health risk to humans, dogs, or cats. Public health officials advise against handling any sick or visibly infected wild animal, but the risk associated with this particular rabbit virus is limited to lagomorph populations.