Overview

• Recent sightings of gray squirrels with wart-like, oozing growths have resurfaced across the United States and parts of Canada, with photos and reports dating back to 2023 and spiking again this summer.
• Wildlife specialists say the lesions are consistent with squirrel fibromatosis, a leporipoxvirus that produces skin tumors which often resolve without treatment in four to eight weeks, though severe cases can be fatal.
• Transmission occurs through direct contact with lesions or saliva and via biting insects such as mosquitoes and fleas, and concentrated feeding at backyard bird feeders can accelerate spread among squirrels.
• Agencies urge residents not to handle or try to capture affected animals and to manage feeders to reduce crowding, noting the viruses are not known to infect humans, dogs, or birds.
• Separately in Colorado, officials have identified Shope papillomavirus in Fort Collins cottontails, a rabbit-only disease that causes horn-like growths and is unrelated to the squirrel cases.