Dartmoor Pony Heritage Trust is trying to contain the outbreak within the 450 hectare site at Bellever, near Postbridge.
Visitors of Dartmoor are being urged to stay away from its native ponies to help stop the spread of a vicious new strain of strangles.
Ponies have already been known to suffer from the highly contagious infection, and now the Dartmoor Pony Heritage Trust is putting a firewall around the 450 hectare site it leases from Forestry England at Bellever to try and protect its herd of 27 ponies which they hope will prevent the infection from spreading further to other herds on the moors.
The site is very popular with visitors but with ponies at Haytor and Widecombe already infected it is urging the public to stay away from its ponies and horse riders to stay out of Bellever.
The charity’s CEO Dru Butterfield said: “The neighbouring newtake to the land we lease has contracted strangles, this strain is particularly nasty.
“We are devastated that our herd, which we go to such extreme measures to care for are now almost certain to contract this terrible infection.
“We urge the public to avoid any contact with our ponies and to please enjoy them from a distance.
“If you are a horse owner we would ask you to avoid Bellever until we provide an all clear notice.”
The DPHT is said to be working closely with leading veterinary experts and the Dartmoor Livestock Protection Society in the hope it can prevent more ponies suffering.
If you see a pony with a snotty nose, coughing or with abscesses please keep away but report the incident to Karla McKechnie Dartmoor Livestock Protection Officer on 07873587561.