Wildlife officers in Fort Collins, Colorado, confirmed that the rabbits alarming residents with horn-like facial growths were infected with Shope Papillomavirus, a rare virus that produces wart-shaped tumors. A photograph posted online in early 2024 showed a cottontail with black spires protruding from its snout, and social-media users compared the animal to creatures from the television series The Last of Us.
“I thought it would die during the winter, but it didn’t. It came back the next year, and it grew,” said Susan Mansfield, a Fort Collins resident who observed one afflicted rabbit for two seasons. She described the growths as black spikes or toothpicks sticking out around the mouth. Users dubbed the creatures Frankenstein bunnies, demon rabbits, and zombie rabbits.
“The growths are caused by Shope Papillomavirus, or Cotton Rabbit Papillomavirus, and if you give it time, it’ll eventually fall off and the rabbit will be fine,” said Colorado Parks and Wildlife spokeswoman Kara Van Hoose, according to LadBible. She noted that about 35 percent of infected rabbits shed the tumors within six months and that euthanasia was recommended only when the masses blocked eating or drinking. Van Hoose added that the bumps were generally benign in rabbits.
The horn-like structures were wart-like tumors that formed when the virus triggered skin cells to grow into dark, tentacle-shaped masses. When these appeared around the eyes, nose, or mouth, the animal could struggle to see or feed, sometimes leading to starvation. Transmission peaked in summer because fleas, ticks, and mosquitoes that carried the virus were most active during warm months. Specialists warned that the insects could also infect domestic rabbits, where the disease was more serious and could progress to lethal carcinomas, and advised keeping pets indoors during summer and autumn.
Virologist Richard E. Shope first described the virus in 1930, and subsequent research helped illuminate links between papillomiruses and cancer. Later DNA studies revealed similarities between Shope papillomavirus and human papillomavirus.
Van Hoose stated that the virus could not spread to humans, dogs, or cats, though deer and elk could contract a separate strain. She acknowledged that the unsettling appearance of infected rabbits may have contributed to the North American legend of the jackalope, an antlered rabbit first depicted in 16th-century illustrations.
Authorities advised residents to observe the animals from a distance and to scare them away with noise if they approached homes. Colorado Parks and Wildlife also encouraged pet owners to use insect control measures, while scientists emphasized that the virus was well known, rarely fatal, and usually self-limiting.
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