Squirrelpox Virus
Every animal species has a host of naturally occurring diseases from which they can suffer, but without posing an overall threat to their population. This is due to degrees of immunity gained from thousands of years of co-evolution; allowing the animal and disease to co-exist. However, when a population is exposed to a new virus that it has not evolved alongside, the impact can be massive.
Squirrelpox virus (SQPV) is a virus that has emerged in red squirrel populations in England since the appearance of the grey squirrel. All evidence suggests that SQPV was brought into the UK with the grey squirrel when it was introduced from America. This virus does not affect grey squirrels, but is lethal to red squirrels on an epidemic scale. Grey squirrels act as a vector (a carrier), transmitting the virus to red squirrel populations. Once a local red squirrel population is infected, the virus can pass from red to red.
|
|
|
|
Micrograph showing a squirrelpox virus particle (virion) in a sample from a grey squirrel
|
Micrograph showing a squirrelpox virus particle (virion) in a sample from a red squirrel
|
|
Micrographs reproduced by courtesy of David Everest of the Veterinary Laboratories Agency Weybridge. The first case of pox infection in the red squirrel was identified using elecron micrscopy at the Veterinary Laboratories Agency (CVL Weybridge) from an animal in Blickling Park, Norfolk by Scott, A.C., Keymer, I.F. and Labram, J., (1981) Vet. Rec. 109 (10) 202.
|
Symptoms: SQPV is typically lethal to red squirrels within two weeks of unset. First symptoms include lethargy and poor coordination, with swelling and lesions soon developing around the eyes, nose, mouth, ears, paws and genitals.
The virus weakens and physically impairs the squirrel making it difficult to feed and vulnerable to predators. The open wounds and lesions increase susceptibility to secondary infections; these are usually a major factor attributing to death.
|
|
 |
|
Red squirrel killed by squirrelpox virus - note sores/lesions around eyes, nose and mouth
|
Alive red squirrel suffering from squirrelpox virus
|
Click here to view the national squirrelpox virus map
Click here to view the spread of squirrelpox virus in Northumberland
Click here to view the spread of squirrelpox virus in Cumbria
Dealing with an SQPV outbreak: Be vigilant for signs of the virus and sick red squirrels at all times, and especially when grey squirrels have been sighted in a red squirrel area. Please report any signs of sick red squirrels to the Save our Squirrels team immediately. The Save our Squirrels SQPV outbreak protocol provides practical advice on all aspects of dealing with an SQPV outbreak. If you find a dead red squirrel, it can be sent away for post-mortem examination to tell us exactly how the squirrel died, and confirm whether it has squirrelpox virus. The cost of the post-mortem is covered by the Defra Diseases of Wildlife Scheme. Please consult these guidelines on sending dead red squirrels for post-mortem.
If supplementary feeding is taking place in the vicinity of an SQPV outbreak, feeders should be removed immediately and disinfected as they may otherwise be a point of virus transmission. Alternatively, the attraction of food can make it easier to spot sick reds or grey squirrels - in this case, we recommend that food is scattered diffusely on the ground, and that feeding sites are monitored regularly.
Adenovirus: Adenovirus is an enteritic viral infection that has been found in red squirrels. Adenovirus infection is associated with diarrhoea, scouring, and poor body condition, and is thought to particularly affect juvenile red squirrels. If you find a sick or dead red squirrel showing either these or other suspicious symptoms, please contact us immediately. Unlike squirrelpox virus, adenovirus is thought to be a natural disease of red squirrels, and current screening and research is helping us to learn more about this virus.
Click here to the national adenovirus map
Research and future hope: Although a lot remains unknown about SQPV, such as the specific method of transmission between individuals, scientific research and virus surveillance programs are providing answers all the time. A specific virus transmission study is currently working to answer questions regarding SQPV transmission, and could be important in directing how we deal with SQPV outbreaks.
Scientists have successfully developed an immuno-contraceptive that sterilises male grey squirrels preventing them from reproducing. However, research is still underway to find a successful system for delivering the immuno-contraceptive to squirrels in the wild.
Work has also begun attempting to develop a vaccine to help protect red squirrels from the squirrelpox virus. However, developing a vaccine is only the first hurdle. As has been the case with the immuno-contraceptive work, a potentially harder task will be developing an affective system to inoculate wild red squirrels with the vaccine - how do we get the science to the squirrels?
A ‘bait delivery system' (where the drugs are provided in food) is the most likely method for delivering both the immuno-contraceptive to greys and the vaccine to reds. Although this sounds straightforward in theory, it is very difficult to achieve in practice. In developing a bait delivery system, it must be ensured that; i) a squirrel feeding on the bait ingests a high enough dose of the drug, ii) the drug dose not require a booster to remain effective over subsequent years, and iii) the drugs reach a high enough percentage of the population to have an overall net benefit.
It may take as long as 10 years before either a vaccine or immuno-contraceptive have been developed to the stage where they can be used to treat wild squirrel populations. In the meantime more traditional conservation methods, such as habitat and population management, are vital in protecting existing red squirrel populations.
|
