The Squirrel parapoxvirus is a virus that is fatal to red squirrels. It is often carried by grey squirrels, who rarely die from the disease.

Grey squirrels rarely die from the disease because they have developed antibodies to help fight it off; however, they can still be carriers of the disease. In sharp contrast, there are no known red squirrels that have developed immunity to the disease, and the mortality rate for infected squirrels in the wild appears to be 100%^[1]; most die within 4-5 days of being infected^[2].

The virus can spread through contact with the infected lesions or contaminated crusts. Parapoxvirus is highly resistant to drying, which results in the ability for crusts to remain contaminated after long periods of time. It is believed that the virus can be transferred through feeders, which is why red squirrel preservation organizations often recommend that feeders are disinfected daily. Parapoxvirus is zoonotic, and it has been reported in man

Symptoms

In red squirrels, the virus causes skin ulcers , lesions, and scabs. It can also cause swelling and discharge (from the lesions/scabs) near the eyes, mouth, feet, and genitalia. Additionally, squirrels that fall victim to the disease often become increasingly lethargic as it progresses.

Infected animals are said to resemble rabbits with myxomatosis, in that they are sometimes found shivering and lethargic.

Origins

The origins of the parapox virus are mostly unknown. The first confirmed incident was in East Anglia in the 1980s. It has since spread to Lancashire (confirmed in 1995-1996), Cumbria (spring 1998), Durham (1999), and Northumberland (1999). The parapox virus is regarded as a significant factor in the decline of red squirrel populations in the UK.

Although the parapox virus has only been recorded once in Scotland, it may be more prevalent due to lack of thorough testing.

Long-term effects

Although red squirrels were once prevalent throughout the British Isles, there are now only about 160,000. Most of these are in Scotland. The decline of red squirrels is blamed mostly on disease, the loss of woodlands, and competition by grey squirrels. There are over 2.5 million grey squirrels in the British Isles. Red squirrels' survival chances in conifer woods are much higher than in deciduous woods.

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Notes

• Kaaden O-R: Infektionen und Krankheiten durch Pockenviren. In: Medizinische Mikrobiologie, Infektions- und Seuchenlehre, ed. Mayer A, 7ed., pp 158-174, Enke Verlag, Stuttgart, Germany 2002 (from [3])