Red Squirrels have had a history of large population fluctuations due to lots of factors, but a major one is disease. The UK has proved a difficult habitat for Red Squirrels. Culling because they were regarded as pests almost made them extinct, with numbers only coming back because of Red Squirrels introduced from other countries. Their habitat has also been depleted by humans as forestry practices have changed. All of these factors are a source of stress to Red Squirrels, and stressed animals tend to be thinner and weaker than those in good habitat. Without disease, this might not be too much of an issue, but when Red Squirrels get infected, their weakened bodies can't cope and they will often die.
1. Red Squirrel population weakened by poor habitat and culling in the past
2. Poxvirus (Squirrelpox) is just one of the diseases the weakened population has been susceptible to
3. Their population has fluctuated greatly in the past, almost dying out at times, which shows they struggle to survive in the UK habitat
4. Weakened Red Squirrels die before they build up immunity to the disease
5. They need good habitat so they are stronger and healthier to fight disease
Poxvirus (or Squirrelpox as it is often called) is by no means the only disease which can kill Red Squirrels. They have also died from Coccidiosis and more recently Enteric Adenovirus is thought to have been a cause of at least one confirmed Red Squirrel death. Poxvirus is the most common disease at the moment, and displays symptoms not unlike myxomatosis in rabbits. At first the squirrel will seem lethargic and probably display poor coordination. As the disease takes hold, lesions will appear around the eyes, mouth, feet and genitals.
It is a common mistake that Grey Squirrels are responsible for Poxvirus. Research has shown that Red Squirrels were dying of a disease between 1900 and 1920. Descriptions of the disease give very similar clinical signs to the disease that scientists now know to be poxvirus. Most of the Red Squirrels reported to be dying had never had any contact with Grey Squirrels. We'd only spread across 4 out of 40 districts while Red Squirrels were fairly common across the country.
Why don't Grey Squirrels catch Poxvirus?
The answer is that Grey Squirrels do catch Poxvirus. However, having a habitat more suitable to us, and being physically larger with better fat reserves, we are more able to survive the disease.
Why don't Red Squirrels have immunity to Poxvirus?
Red Squirrels are living right on the edge of their natural habitat, which extends from the UK all the way to the far east. The UK habitat isn't all that suitable, and is getting less and less suitable as humans alter the forest landscape significantly. So they tend to be struggling constantly just to survive, and when they catch Poxvirus, they usually die before their immune systems can build up immunity to the disease. It is entirely possible for them to survive the disease. Indeed, the Zoological Society of London has identified eight cases in which free-living red squirrels have survived infection.
If large numbers of Red Squirrels are to fight this disease themselves, they need good habitat, with plenty of food and shelter, so emphasis on planting more coniferous forests is important. The development of a vaccine which could be given to live-trapped red squirrels before they are released again could be a way in which humans could also help the reds further.
Want more information on SQPV?
We have a much more detailed analysis of the currently available scientific research studying SQPV. It is rather a long read, but for those interested in the scientific detail, it is definitely well worth the read. We have done our best to keep it readable for everyone, explaining the complex terms which would normally just be dropped straight into a research paper.
Native by Birth - Condemned by Origin