Squirrel pox & diseases

Red squirrel suffering with squirrel pox by Lisa Fuller

Squirrel pox can be devastating for red squirrel populations. Its spread into red squirrel areas is linked to grey squirrels invading red squirrel areas.

The virus is almost always fatal to red squirrels and an outbreak can wipe out the majority or all of a local population. Grey squirrels rarely contract the disease, but can be host to high concentrations of the virus that they can transmit to red squirrels. In the presence of squirrel pox, research shows red squirrels die out 17-25 times faster than by competition from grey squirrels alone.

Squirrel pox outbreaks in red squirrels do not occur in areas that grey squirrels have not yet reached, e.g. northern Scotland. Outbreaks are linked to grey squirrels encroaching into red squirrel areas, but red-to-red transmission can occur following this. Further research is being conducted to understand the factors involved in its transmission.

The virus is found in bodily fluids but is fairly resilient, so can survive outside a host for a relatively long time. Transmission vectors include physical contact, contaminated objects/areas and shared parasites.

Red squirrel suffering with squirrel pox by Sarah McNeil


Signs that an individual is infected are said to be similar to those seen in rabbits with myxomatosis:

● Ulcers, lesions and scabs around the face, feet and genitalia

● Pussy discharge from the ulcers, lesions and scabs

● Swelling

● Lethargy

● Lack of coordination

● Drinking large quantities of water

Infected individuals can take up to two weeks to die, often starving to death as they are unable to feed themselves.

What to do

If you see an infected squirrel please report it as soon as possible to the local red squirrel group for that area. Sightings of grey squirrels in red squirrel areas should also be reported. See our volunteering page, under get involved, for links to groups across the UK.

People are advised not to feed squirrels during squirrel pox outbreaks. Feeders can bring infected and healthy individuals into contact with each other, and increase the spread of the disease across the population. At all other times feeders should be cleaned regularly.


From 2009, the Moredun Institute conducted work on a vaccine for squirrel pox, but it resulted in severe side effects in red squirrels and requires modifying. No further vaccine research has been carried out since 2013.

Those interested in activity around a red squirrel vaccine should contact the Wildlife Ark Trust, as they are leading on the project.

Other diseases

There are other diseases to be aware of that can seriously affect red squirrels, but they do not have the same devastating impact on populations that squirrel pox does.

  • Adenovirus: produces lesions in the digestive tract and internal bleeding, which can be fatal. This is of particular concern to captive bred red squirrels, so health screening checks must be carried out before they are released as part of reintroduction and reinforcement programmes.

  • Leprosy: causes loss of hair and swelling in the face, ears, genitalia and feet; the skin can look warty. Red squirrels can live for extended periods with the disease, as it takes a long time to progress. Symptoms are sometimes mistaken for squirrel pox lesions, but leprosy does not rapidly kill off large proportions of a population.