EXPERTS have warned of the challenges of trying to contain a virus which can be deadly to red squirrels without controlling numbers of their grey counterparts.

New research predicts that squirrelpox could spread right through the grey squirrel population of between 200,000 and 300,000 in Scotland, unless numbers are more strictly controlled.

But the work by Professor Andy White, Professor of Mathematics, Heriot-Watt University, and ecologist Dr Peter Lurz suggests that the endangered 120,000 red squirrels are unlikely to be affected unless greys invade their territories en masse.

The virus is carried by grey squirrels without them manifesting any symptoms, but the reds experience severe illness and normally die.

Professor White said the real danger was if there was an uncontrolled invasion of the reds' territory in areas such as Highlands, Tayside, Argyll, Moray and Aberdeenshire, so increased vigilance was required.

He said: "Without grey squirrel control, the virus will likely continue to spread across all areas where grey squirrels exist.

The key is to remain vigilant for grey squirrels trying to colonise these areas."