A virus capable of devastating rare red squirrel populations has reached one of the species' UK strongholds for the first time.
By Alex Kirby
BBC News Online environment correspondent
It is killing squirrels in Merseyside in north-western England, near the city of Liverpool.
The virus, parapox, which kills the animals within weeks or even days, seldom responds to treatment.
It is carried by grey squirrels, though they are seldom harmed by it; the reds have no immunity.
The origins of parapox are unknown, but some grey squirrels are known to carry antibodies.
Red squirrels with the virus will have wet, discharging lesions or scabs around the eyes, mouth, feet and genitals.
Infected animals resemble rabbits with myxomatosis, and are sometimes found shivering and lethargic.
The Merseyside red squirrel population lives in Sefton, an area stretching along the Lancashire coast from Southport down to Bootle.
A dead animal found there was taken for analysis to Liverpool University and found to have been killed by the virus. Another dead squirrel is suspected of having parapox.
Red squirrels are declining fast (Image: Kevin Cook)
There are thought to be no more than 600-1,000 red squirrels in the area.
In 1995 a nearby colony living around the town of Ormskirk was also affected by parapox, and hardly any red squirrels are left there.
Steve White is the conservation officer for the Wildlife Trust for Lancashire, Manchester and North Merseyside.
He told BBC News Online: "Red squirrels are declining catastrophically in the UK.
"The Sefton squirrels have done fairly well, because they thrive in the pinewoods there, which the greys don't like so much.
"The reds have also been protected by the arable farmland behind the pinewoods. But we think the greys are crossing that now and taking the virus to them.
"So we're asking people to let us know about any sick or dead red squirrels they may find, and also any greys, so we can trap them.
"We don't want people to touch sick or dead animals, because we don't know whether humans can also carry the virus."
Feeding squirrels can imperil them
The trust is urging people who feed red squirrels in their gardens to disinfect feeding equipment regularly.
Red squirrels were once widespread throughout the British Isles, but now there are only about 160,000, most in Scotland.
Hope in the pines
The number in England is about 30,000, most of those in the north. There are around 10,000 on the Welsh island of Anglesey, and some on the Isle of Wight and Brownsea Island in the south of England.
Their decline is blamed on disease, the loss and fragmentation of woodlands, and competition by the greys, which now number more than 2.5 million.
They can exploit deciduous woodlands better than the reds, and their breeding prospects and adult survival rates are better there.
In conifer woods, though, the reds' survival chances are much higher.