Pox Virus Threatens Red Squirrel
Introduced Grey Squirrel Carries Disease That Kills Native Species
The grey squirrel (Scurius carolinensis), introduced into the UK in the mid-nineteeth century is now well on its way to eliminating the red squirrel (Scurius vulgaris) from England. A pox virus brought into the UK by the introduced alien squirrel species is proving deadly to the natives squirrels.
Introduced Alien Species Often Create Problems for Native Wildlife
Man has long been in the habit of moving plants and animals around the globe. Early explorers brought home samples of every new species they came across. Some died out, but the ones who survived are, for the most part, thriving in their new environment.
The species that thrived have several things in common. They are highly adaptable species, with less stringent habitat and dietary needs. In addition, they don’t experience the same level of predation in their new environment, allowing them to flourish and outcompete local native wildlife. Worse yet, they often carry diseases to which they have an immunity. Native species, exposed for the first time to these diseases have no immunity. The result is that the natives die off when exposed to the interlopers.
Grey Squirrels are Pox Virus Carriers
We now know that disease plays a part in the serious decline in the UK red squirrel population. Grey squirrels are carriers of squirrel pox virus. As a carrier, the grey squirrel brings pox virus with it but does not get sick unless it is highly stressed by overcrowding, lack of food or other environmental pressures. The red squirrel appears to have no immunity.
Red squirrels that are exposed usually die, unless they can be captured and treated within the first few days of showing signs of disease such as slowness and uncoordinated movement. By the time the animals show lesions (sores on the genitals and face, especially around the mouth, nose and eyes), they are doomed.
Modes of Transmission
How do red squirrels catch the virus from grey squirrels? That is not known for certain. Possibilities include direct contact between the two species, virus remaining in habitat such as drays (nests), arthropod vectors (fleas) being an intermediate host or urine and/or feces serving as the reservoir. The Scottish Squirrel Group (a combination of government organizations and local voluntary squirrel groups overseen by Scottish Natural Heritage and the Forestry Commission) is funding a research project to determine how the disease is transmitted. This will guide them in their efforts to slow the spread of grey squirrels (and squirrel pox) into Scotland.
Once the mode of pox transmission is known, efforts can be made to reduce the chance of the virus affecting red squirrel populations. Sadly, one thing that will have to happen is that grey squirrels numbers will have to be reduced in order for the red to survive.
Native English Red Squirrel
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American Grey Squirrel
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