As if black-horned rabbits weren’t strange enough, people are now spotting zombie-like squirrels covered in odd, sometimes bleeding sores in their backyards and parks. These sickly squirrels aren’t zombies, however, but victims of a real viral disease.
Residents in both Canada and the U.S. have recently reported sightings of the zombie squirrels, dating back to at least 2023. These animals are likely carrying a germ known as the squirrel fibroma virus (SFV). Though the condition is scary-looking, squirrels usually recover from the infection, and it poses no threat to humans.
SFV was first discovered in the 1950s and is a poxvirus, meaning it’s related to the virus that causes smallpox in humans. That said, it’s a part of a genus, leporipoxvirus, whose only known natural hosts are squirrels and rabbits. The infection causes benign tumors, or fibromas, to form across the squirrel’s skin, particularly on its head or limbs.
The virus is thought to primarily spread through the bites of mosquitos and fleas, but it may also be transmitted through close direct contact with an infected squirrel. It predominantly affects gray squirrels, though it can infect other species as well.
SFV can be a dangerous disease for squirrels. The tumors can potentially metastasize to the animal’s internal organs or become so large and numerous on the skin that they cause secondary infections or even hamper the animal’s vision and ability to eat. But according to the Michigan Department of Natural Resources, the infection typically doesn’t cause any obvious signs of illness outside of the skin fibromas. And in areas where it is common, like Michigan, the virus hasn’t had any effect on the overall squirrel population. In most cases, the fibromas regress over time, and the animal recovers completely.
If you’re a hunter with a hankering for squirrel meat, you can also rest easy. Even SFV-infected squirrels are apparently safe for consumption, according to the Michigan DNR. Still, the average person shouldn’t try to touch or handle infected squirrels, or really any wildlife for that matter.
On a little side note, SFV is sometimes called the squirrel pox virus. But this is also the nickname for a different pox virus (the squirrelpox virus) that predominantly affects squirrels in the UK. Adding to the confusion, researchers have identified other potential squirrel pox viruses in countries like Canada and Germany. All of which is to say: It feels like there should be a cleaner labeling system for these squirrel-related diseases.
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