Deer across the United States have been photographed with large, tumour-like growths hanging from their faces and bodies, alarming local residents and sparking fresh warnings from wildlife officials about the growing impact of climate change on animal disease.
Images shared on social media in recent weeks show white-tailed deer in New York, Pennsylvania and Wisconsin covered in bulbous grey and black swellings. Experts say the condition, known as deer cutaneous fibroma – or “deer warts” – is caused by a papillomavirus spread primarily through biting insects such as mosquitoes and ticks.
The growths, which can range in size from a pea to a football, usually subside within months as the animal’s immune system suppresses the virus. While rarely fatal, severe cases can interfere with feeding or vision, and secondary bacterial infections sometimes occur.
Kristin Mansfield, a wildlife veterinarian in Washington state, said the virus can also pass between deer through direct contact at feeding sites, bedding areas or territorial rubbing posts. “It’s a disease that has always been present, but conditions this summer have been particularly favourable for spread,” she said.
Researchers warn that warmer temperatures are lengthening the breeding season of insects that carry disease, allowing viruses to spread into new regions.
“These temperature changes are resulting in diseases that were never endemic in certain areas becoming endemic,” said Dr Omer Awan of the University of Maryland School of Medicine. He noted that Lyme disease, transmitted by ticks on deer, is now appearing in parts of southern Canada and the northern US where it was once unknown.
Although the fibromas pose no risk to humans, the deer that carry them may bring other tick-borne illnesses closer to populated areas. Scientists add that social media is also playing a role in raising public awareness, with more sightings shared online than in previous decades.
