While rabbits do not naturally grow horns, horn-like growths can appear on them due to a scientific phenomenon. These unique protrusions are not true horns, but keratinous tumors or warts. This condition results from a specific viral infection.
The Viral Origin of Rabbit “Horns”
The horn-like growths on rabbits are caused by the Shope papillomavirus (SPV). This virus infects rabbit skin cells, leading to an uncontrolled proliferation of these cells. The resulting growths are benign tumors or warts, composed of keratin.
These keratinous growths can appear in various locations on an infected rabbit, often on or near the animal’s head, including the face, neck, shoulders, eyelids, and ears. They can also be found on the rabbit’s feet. The size of these growths can vary significantly, ranging from small lesions to prominent, dark, horn-like structures several centimeters in length.
How the Growths Affect Rabbits
These growths can significantly impact a rabbit’s well-being. Depending on their size and location, the tumors can interfere with essential bodily functions. For instance, growths around the mouth can make it difficult for the rabbit to eat. Growths near the eyes can impair vision.
The growths can also increase a rabbit’s susceptibility to other health problems. Larger tumors can be prone to injury, creating open sores vulnerable to secondary bacterial infections. While generally benign, papillomas can transform into aggressive squamous cell carcinomas, a type of skin cancer. This progression to cancer occurs in approximately 25% of cases in cottontail rabbits and up to 75% in domestic rabbits. If these malignant tumors spread, they can metastasize to internal organs like the lungs, lymph nodes, kidneys, and liver.
Understanding Transmission and Occurrence
The Shope papillomavirus primarily spreads among rabbits through the bites of arthropod vectors, such as mosquitoes and ticks. These insects transmit the virus from an infected rabbit to an uninfected one during feeding. Direct contact with infected animals or contaminated environments can also contribute to the virus’s spread.
This virus is most commonly found in wild cottontail rabbits, particularly the Eastern cottontail rabbit (Sylvilagus floridanus), which is considered its major natural host. While the virus predominantly affects wild populations, it can also infect other leporids, including brush rabbits, black-tailed jackrabbits, snowshoe hares, European rabbits, and domestic rabbits. However, the incidence of this disease is rarer in domestic and laboratory rabbits compared to their wild counterparts.
From Science to Folklore: The Jackalope
The unusual appearance of rabbits with horn-like growths likely served as the inspiration for the popular folklore of the jackalope. This mythical creature, often depicted as a jackrabbit with antelope horns, is a well-known figure in North American tall tales. The scientific reality of the Shope papillomavirus provides a tangible link to how such a legend might have originated.
Historical accounts and illustrations of horned rabbits date back centuries, appearing in scientific treatises from the 16th and 17th centuries. These early depictions suggest that the phenomenon of rabbits with these growths has been observed for a long time. In the 1930s, American virologist Richard E. Shope investigated reports from hunters in Iowa about rabbits with “horn” protrusions. His research led to the discovery of the Shope papillomavirus in 1933, confirming that these growths were keratinous carcinomas caused by a viral infection. This scientific discovery provided a biological explanation for the fantastical horned rabbits, connecting a real-world observation to the enduring jackalope legend.