An outbreak of Squirrelpox virus has been detected in red squirrels near Dumfries.
Conservationists have warned it could have serious consequences for the red squirrel population in Heathhall Forest.
They said several animals have been spotted in the forest with classic signs of the disease which is usually fatal within two weeks.
Symptoms include weeping lesions on the face, paws and genitalia.
Conservation group Saving Scotland's Red Squirrels said the symptoms prevent the squirrel from eating, drinking or moving.
The pox is carried by grey squirrels but is deadly only to native reds.
Wildlife feeder boxes are a breeding ground for the disease as they bring both species into closer contact.
Stephanie Johnstone, a conservation officer with the squirrel project, said feeder boxes have been removed from the forest in a bid to contain the spread of the virus.
She said: "In conjunction with Forestry Commission Scotland, who manage Heathhall, we have deployed emergency Squirrelpox outbreak response measures.
"All feeder boxes found on site have been removed and trapping has commenced to isolate any sick red squirrels and remove any grey squirrels.
"Captured sick red squirrels will be taken to a local veterinary clinic in Dumfries where they will be assessed and either treated or euthanised.
"There are very few instances of red squirrels surviving the disease. Nonetheless, the South West Scotland Wildlife Hospital is on standby to receive any sick red squirrels into their isolation unit if a vet deems that they may have a chance of recovery."
Local people have been asked to remove any feeder boxes placed in the forest and the surrounding area.
They have also been asked to ensure any feeders in their gardens are regularly and thoroughly cleaned with an anti-viral solution.
Squirrelpox is not harmful to humans but anyone who spots a sick squirrel should not approach it, but contact the project for advice.