After recent reports of rabbits and squirrels developing tumor-like growths, similar deformities seen in deer across parts of the United States have raised fears of a potential outbreak.

Over the past several months, white-tailed deer with large wart-like growths have been photographed in states including New York, Pennsylvania, and Wisconsin. One Reddit user, sharing an image of a deer in Pennsylvania, asked: “But what is the growth? Is it a mole? A boil? An injury?”

What Is Causing the Growths?

According to wildlife officials, the unusual appearance is the result of a viral condition known as deer cutaneous fibroma, commonly referred to as “deer warts.” The disease is caused by a virus spread among deer populations throughout the U.S.

Transmission occurs primarily through disease-carrying insects such as mosquitoes and ticks, which transfer the virus when feeding on blood. Direct contact—such as rubbing against an infected deer or contaminated surface—can also spread the disease.

The virus belongs to the same broad family as papillomaviruses, which affect humans by targeting the skin and mucous membranes. However, experts emphasize that humans cannot contract deer warts directly. The greater concern lies in the ticks carried by deer, which can transmit illnesses like Lyme disease to people.

Climate Change and Disease Spread

Dr. Omer Awan of the University of Maryland School of Medicine told The Mail that environmental shifts may be contributing to the spread of tick-borne illnesses into new areas.

“These temperature changes are resulting in diseases that were never endemic in certain areas to become endemic,” Awan explained. “If you take a look at Lyme disease, for example, we’re starting to see it in places we never saw it before — including southern Canada and northern U.S. states such as Maine.”

Impact on Deer

The fibromas typically develop on a deer’s head, neck, and forelegs. While they are not painful, the growths can hinder basic functions such as eating, walking, or even seeing if they grow too large.

Fortunately, the condition is usually temporary. The fibromas often dry up and fall off naturally within a few months. One social media user noted: “This deer in my yard… [the warts] got worse, then three months later, they were gone.”

A Long-Standing Virus

Although the appearance of these growths has alarmed many who encounter them for the first time online, experts stress that deer cutaneous fibroma is not new. Records suggest the virus has circulated in U.S. deer populations since at least the 1950s.

Increased public awareness—driven by social media images—has simply brought a long-existing wildlife disease into sharper focus.