A growing number of rabbits in Colorado have been spotted with dark horn-like growths on their heads, earning them the nickname “Frankenstein rabbits”.

These strange appearances are caused by the Shope papillomavirus, which triggers tumor growth around the heads of cottontail rabbits.

According to wildlife sources, the virus is transmitted by parasites such as ticks and fleas, which spread it through their bites.

The virus was named after Richard E. Shope, a professor at Rockefeller University, who first discovered the disease in the 1930s.

“Rabbits are usually infected during the warmer summer months when the virus is spread by insect bites from fleas and ticks,” a Colorado Parks and Wildlife spokesperson said.

The effects can be deadly for rabbits, as the growths can enlarge to the point of preventing them from eating, leading to starvation.

Experts note that the disease tends to be more severe in domestic rabbits than in wild ones, with the greatest concern being the development of serious and potentially fatal skin cancer.