Squirrel pox is a viral disease that is almost always fatal to red squirrels, killing nearly 100% of infected animals within one to two weeks of symptoms appearing. It is caused by the squirrelpox virus (SQPV), the sole member of the genus Sciuripoxvirus in the poxvirus family. The disease has become one of the biggest threats to red squirrel survival in the UK and Ireland, largely because grey squirrels carry the virus without getting sick and spread it wherever the two species overlap.
Why Grey Squirrels Spread It but Don’t Get Sick
Grey squirrels are the natural reservoir for squirrelpox. When they carry the virus, the infection is subclinical, meaning it rarely produces visible disease. They go about their lives normally while shedding virus into the environment. Red squirrels, on the other hand, have no natural resistance. When they encounter the virus, the results are devastating.
This dynamic is what makes squirrelpox such a conservation crisis. Grey squirrels were introduced to the UK from North America in the 1800s and have been displacing red squirrels through competition for food and habitat ever since. Squirrelpox accelerates that displacement dramatically: in areas where grey squirrels carry the virus, red squirrel populations collapse far faster than they would from competition alone.
How the Virus Spreads
Squirrelpox spreads through three main routes: direct contact between infected animals, viral particles shed into the environment through urine and droppings, and parasites like fleas that feed on both species. The parasite route appears to be especially significant. In one study, every single parasite collected from an infected red squirrel tested positive for viral DNA, and 27% of fleas taken from infected grey squirrels also carried the virus.
Urine is another important transmission pathway, particularly during warm, dry summer conditions when viral particles survive longer on surfaces. Shared feeding stations, where both species visit the same food source, create an ideal environment for indirect transmission through contaminated surfaces, droppings, and urine residue.
What Squirrel Pox Looks Like
In red squirrels, squirrelpox causes visible skin lesions, ulcers, and swelling, particularly around the eyes, mouth, feet, and genitals. Infected squirrels often appear lethargic and may have weeping or crusted sores. The swelling around the eyes can become severe enough to impair vision, making it difficult for the animal to find food or avoid predators. Once symptoms appear, death typically follows within one to two weeks. There is no effective treatment for infected wild red squirrels.
Grey squirrels occasionally develop mild skin lesions, but the infection resolves on its own. Most show no symptoms at all.
Risk to Humans and Pets
There is no known risk to humans from squirrelpox. The virus is specific to squirrels and does not infect people or domestic animals. That said, washing your hands after handling any wild animal or cleaning feeders is still good practice, since squirrels can carry other pathogens.
Keeping Feeders Safe for Red Squirrels
If you feed red squirrels in an area where grey squirrels are also present, feeder hygiene is critical. During a confirmed squirrelpox outbreak, feeding stations should be shut down entirely. You can scatter feed instead, which avoids concentrating animals at a single contaminated point.
Outside of active outbreaks, clean feeders at least every two weeks in areas where both species are present. The process involves scrubbing with a mild, low-perfume detergent and water to remove greasy residue, then rinsing and soaking the feeder in a 5 to 10% bleach solution (sodium hypochlorite) for 10 to 15 minutes. Rinse again with clean water and let it dry completely before refilling. Wear waterproof nitrile gloves for the entire process.
A few additional practices help reduce risk. Rotate feeders between two or three locations on your property each month, so no single spot accumulates viral contamination. Keep enough feeders on hand that cleaned ones can rest and dry while others are in use. Remove any uneaten or spoiled food promptly. Avoid ammonia-based disinfectants, which can mimic urine scent marks and alter squirrel behavior around the feeder.
Vaccine Research and Conservation
Researchers at Bangor University have been developing a vaccine that could protect wild red squirrels from squirrelpox. The concept involves trapping red squirrels in live-cage traps, immunizing them by injection, and releasing them with lasting protection. The vaccine candidates are designed to be simple and inexpensive to produce, non-infectious, and deliverable by trained, licensed operators in the field.
Scaling this approach to wild populations presents challenges. Regulatory hurdles remain, and vaccinating free-ranging animals one by one is labor-intensive. Still, researchers see it as a realistic tool for protecting red squirrel strongholds, particularly in Scotland and parts of Ireland where viable populations still exist but grey squirrels are encroaching. Combined with grey squirrel management programs and habitat protection, a vaccine could be a significant step toward keeping red squirrels from disappearing entirely from the British Isles.