Scotland's red squirrel population is under threat from the virus

Squirrel pox is said to have been carried over the border by grey squirrels migrating north from Cumbria.

Red squirrels with the virus will suffer skin ulcers, lesions and scabs, with swelling and discharge around the eyes, mouth, feet and genitals.

The Moredun Research Institute near Edinburgh found the virus after taking blood samples from grey squirrels.

Grey squirrels are seldom harmed by the virus, but red squirrels have no immunity and usually die within 15 days.

Scientists say it is the first evidence of squirrel pox virus in southern Scotland and has serious implications for the endangered red squirrel population.

They pass it into red squirrels who once the have caught it die within two weeks Elly Hamilton Red squirrel conservation officer

Infected animals resemble rabbits with myxomatosis and are sometimes found shivering and lethargic.

Roger Cook, the chief executive of the European Squirrel Initiative, urged people to report any sightings of sick or dead red squirrels.

Elly Hamilton, a red squirrel conservation officer from the Scottish Borders, said this was the first convincing case of the pox crossing the border.

She said: "All we know is that the grey squirrels carry it. They are unaffected clinically by it so they act as a reservoir host for the disease. They pass it into red squirrels, who once they have caught it, die within two weeks."

The disease was first confirmed in grey squirrels in East Anglia in the 1980s, Ms Hamilton said.

It had been working its way north since, she added.

"It is believed that where grey squirrels are carrying antibodies to this virus that they replace red squirrels 20 times faster than they would do normally."