
In parts of the United States, wild rabbits have started to develop bizarre, tentacle-like growths on their heads and faces. In some cases, they look more like horns.

The cause?

It's an unsettling effect of the Shope papillomavirus (SPV). 

First documented in the 1930s when hunters in Iowa reported “horned” rabbits, the virus causes keratinous carcinomas that can resemble twisted antlers. These growths, which can spread to other body parts, sometimes become so large they prevent the animal from eating, leading to starvation. 

Richard E. Shope’s groundbreaking 1933 research on the virus not only solved the mystery but also provided the first mammalian model for cancer caused by a virus—research that later informed the development of the human papillomavirus (HPV) vaccine. 

The eerie appearance of infected rabbits is also believed to have fueled tall tales about mythical creatures like the jackalope.

The virus spreads mainly through parasites such as rabbit ticks and shows a strong preference for skin tissue, especially on the head, ears, and neck. While many infected rabbits survive, about a quarter of cases turn malignant, with cancer spreading to the lungs, lymph nodes, and other organs. 

SPV has been pivotal in understanding viral replication, immune evasion, and cancer biology. Scientists have even used it to explore antiviral treatments and immune responses in ways that extend far beyond rabbit health. 

Source: 
Shope, R. E. (1933). Infectious papillomatosis of rabbits: With a note on the histopathology. Journal of Experimental Medicine, 58(5), 607–624


A rare virus has caused tentacle-like growths in rabbits across the US