Frankenstein Bunnies and Papillomaviruses

Laurie Anne Walden, DVM

Image by Clinton Forry on Flickr, CC BY 2.0 license

Photos of rabbits with horn-like growths popped up on the internet last month after people spotted the rabbits in northern Colorado. The growths are caused by infection with a papillomavirus, in the same family as the viruses that cause warts and cervical cancer in humans. The virus infecting these rabbits isn’t contagious to other species and usually causes wild rabbits less trouble than you would think.
 
Cottontail rabbit papillomavirus, also called Shope papillomavirus (for the person who first described it), is not a new virus. It’s been identified in museum specimens dating from the early 1900s. Infection is most common in cottontails and other wild rabbits in the midwestern United States. We could speculate that the long skin growths inspired the myth of the jackalope, the fabled jackrabbit with deer antlers on its head.
 
In most wild rabbits, the growths are benign and eventually fall off on their own. Unless the growths interfere with eating and drinking, they don’t usually cause a problem. Infection in domestic rabbits is rare but potentially much more serious. In domestic rabbits, the growths are more likely to become malignant cancers than they are in wild rabbits.
 
Cottontail rabbit papillomavirus is spread by flea, tick, and mosquito bites. The skin growths are in areas most often bitten by insects, which is why most are on the face and head. Because domestic rabbits are at risk of cancer, pet rabbits should be kept indoors in areas of the country where the virus is spreading, especially in the summer and fall when insects are most active.
 
Rabbit papillomavirus infects only rabbits. Humans, dogs, cats, and other species are not at risk from this particular rabbit virus. Humans and other species have their own papillomaviruses, all of which are typically species specific (they aren’t contagious to other species).

​Human papillomavirus (HPV) is the name for hundreds of related viruses that cause various kinds of growths in people. Some of these growths, like common skin warts and plantar warts, are benign. Others, like genital, cervical, anal, and oral lesions, can become malignant cancers. HPV infection is a common sexually transmitted disease in humans.
 
Scientists are very interested in finding out why some virus-related growths are benign but others turn into cancer, a process called malignant transformation. One of the best ways to study malignant transformation in humans is to study similar viruses that cause similar cancers in other animals. And it happens that cottontail rabbit papillomavirus was the first papillomavirus identified and the first shown to cause cancer in a mammal. This is why the virus is also named after Richard Shope, the cancer researcher who discovered it.
 
So the next time you see a social media photo of a Frankenstein bunny, just think “Oh look, a valuable animal model of malignant transformation that helps us diagnose, prevent, and treat HPV and cancer in people.”

Image source: https://www.flickr.com/photos/wd45/364229280, CC BY 2.0

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