Red squirrels show signs of resistance

25 November 2013 by Alex Peel

A small group of survivors has offered red squirrels a glimmer of hope in their on-going battle with squirrelpox.

Healthy red squirrelIn 2008, a Merseyside population of around 1,000 red squirrels was decimated by the deadly disease. Numbers dropped by about 85 per cent.

But preliminary results of a study carried out on the remaining population suggest a few of the animals that were exposed to the disease managed to survive.

A team of researchers, led by Dr Julian Chantrey of the University of Liverpool, took blood samples from around 100 reds from the Formby National Trust reserve in Merseyside.

Less than ten per cent of the animals showed signs of squirrel pox antibodies, suggesting that they had managed to overcome an infection.

In populations where squirrel pox is present, greys replace reds about 20 times faster

- Dr Julian Chantery, University of Liverpool

Since the outbreak, the Merseyside population has recovered, and numbers have now returned to almost 60 per cent of pre-pox levels.

But the picture across the UK remains bleak. Grey squirrels, introduced to Britain from their native North America by the Victorians, have taken most of the blame.

Since around 1945, the greys have been spreading rapidly northwards, forcing the smaller and less adaptable reds into retreat.

Three quarters of the UK's red squirrels now reside on islands or in Scotland. The most southerly populations of reds surviving without intensive protection are around the English-Scottish border.

Studies have suggested that the presence of greys causes fewer female reds to breed, and makes it difficult for juveniles to survive. But Chantery and his team believe that squirrel pox is also playing a vital role in grey supremacy.

Red squirrel with early pox

Red squirrel in the early stages of a squirrelpox infection

"We think the disease is fundamental," he says. "Greys carry it but it seems to cause them no problems - they've evolved with it - so it doesn't affect them as severely as it does the reds."

"In populations where squirrelpox is present, greys replace reds about 20 times faster."

The research was carried out as part of a NERC-funded PhD project, in conjunction with the National Trust and the Lancashire Wildlife Trust.

The team now hopes to secure funding to work out how comprehensive the red squirrels' resistance to the disease has become. Meanwhile, work to develop a vaccine goes on.