An emergency outbreak response has been launched following the death of a number of red squirrels due to suspected squirrelpox.
Saving Scotland's Red Squirrels (SSRS) said it had recently received multiple reports of potential cases in Johnsfield, near Lockerbie in Dumfries and Galloway.
At least 10 red squirrels have since been found dead in the past few weeks.
The virus is carried by grey squirrels but is lethal only to reds.
Symptoms include weeping lesions, which prevent the red squirrel from eating, drinking or moving.
As a result, it is usually fatal within two weeks and an outbreak can cause local numbers to crash.
Andrew Hodgkinson, project officer for SSRS, said: "This is a particularly vulnerable time for red squirrels, as they prepare for the upcoming mating season and increase contact with one another.
"We have deployed our emergency squirrelpox outbreak response measures, and as such locals can expect to see an increased staff and volunteer presence in the area as we increase grey control efforts in the region in a bid to stem the outbreak."
The first known squirrelpox outbreak in Scotland occurred in 2007 near Lockerbie and since then the disease has arisen in various red squirrel populations across the south of the country.
However, despite outbreaks in various areas over the years, targeted grey squirrel control work has been credited for allowing red squirrel populations to successfully recover.
'Squirrelpox outbreak devastating'
Nicole Still, programme manager at SSRS, said: "It is devastating to learn of this squirrelpox outbreak.
"Members of the public can help by reporting all sightings of red and grey squirrels to us via our website, thoroughly cleaning all garden feeders with an anti-viral solution which is available from most local farm supply shops, taking feeders down for two to four weeks, and posting any dead red squirrel carcasses found to the Royal (Dick) School of Veterinary Studies for post-mortem analysis."