Coastal community of red squirrels in NW England show signs of immunity to poxvirus

The red squirrel population which is a feature of the coastal pinewooods at Formby, Merseyside, and elsewhere along this coast is showing signs of immune resistance to the deadly squirrel pox virus transmitted by grey squirrels (who also possess immunity).

The onset of the pox virus in the Merseyside red squirrel population in 2008 had caused around 85% mortality, reducing the surviving population to a dangerously low level, but now there are signs that the surviving population has developed an immune resistance to the deadly disease.

The Guardian reports, 22nd November 2013: “The first case of a wild red squirrel surviving the pox virus carried by greys has been recorded by researchers who have discovered encouraging signs of resistance to the deadly disease. An isolated colony of red squirrels at Formby, Merseyside, were decimated by an outbreak of squirrel pox in 2008, which saw the population crash by 85% to less than 200 squirrels.

“The disease, which is transmitted to reds by grey squirrels who remain unaffected by it, is thought to be a significant factor in the precipitous decline of the much-loved native mammal across Britain. But scientists from the University of Liverpool monitoring the population at Formby have identified individual red squirrels which have contracted but survived the virus.

The red squirrel population is showing signs of bouncing back.
Photograph: Dr Julian Chantrey/Institute of Integrative Biology/University of Liverpool

Dr Julian Chantrey, from the University of Liverpool’s Institute of Integrative Biology, said that while some individuals had survived by chance, blood tests of survivors from Formby found that a small number — less than 10% — had antibodies which would suggest they had recovered from infection in the past. But he warned that this was not yet proof that squirrels were developing immunity to the disease.”Over time, a degree of resistance should become established in the population but this is not yet full immunity,” he said. “The Formby red squirrel population will become infected by squirrel pox again and it will cause significant mortality but hopefully it won’t be as high as 85% next time.”

It is hoped that red squirrels’ resistance to squirrel pox might prove similar to rabbits with myxomatosis, which initially killed around 98% of the rabbit population before the animal bounced back. But Chantrey said the outlook was less positive for red squirrels. The myxomatosis virus became less severe because it was, in effect, destroying itself by killing its rabbit host so effectively. With squirrel pox virus, there is no imperative for it to become less virulent to red squirrels because it lives within the grey squirrel population as well.

Red squirrels have disappeared from much of southern Britain in the last century with the march of the larger North American grey squirrel, which outnumbers reds by 2.5 million to 160,000.

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