Overview

• Photos and reports of gray squirrels with pus-filled growths have surged this summer across the U.S. and Canada, following social media posts that date back to 2023.
• Experts attribute most cases to squirrel fibromatosis caused by a leporipoxvirus and say it is not known to infect humans, pets, or birds.
• Officials advise people not to handle affected animals and to let the illness run its course, noting most recover in four to eight weeks though severe cases can be fatal.
• Transmission likely occurs through contact with lesions or saliva and via biting insects, with backyard bird feeders accelerating spread by concentrating animals.
• Separately, Colorado Parks and Wildlife confirmed Shope papillomavirus in Fort Collins cottontails with horn-like growths, a rabbit-only virus that poses no known risk to people.