In the wake of 48 cases of dog infection and 21 deaths in the past 18 months, vets in the UK are trying to find out the reason behind the mystery.
Half of the confirmed cases have been reported from around the New Forest in Hampshire. Symptoms of the disease are skin lesions on legs and chest, lethargy, loss of appetite and vomiting. Very soon, the disease attacks the kidneys.
Since December 2012, 11 dogs died from the disease after they were taken on walks in the New Forest.
Doctors say the disease is similar to Alabama rot, which was first detected in the US in the 1980s and affected animals' kidneys and then led to death. It is believed to be caused by a rare form of E.coli.
Vet David Walker, who is investigating the mystery illness, said: 'We don't know what the trigger is, which makes it very hard to treat. There's no pattern among dogs that have died."
The latest victim was three-year-old Tegan, a fox terrier, who died after a walk at the Deerleap enclosure near Ashurst in the New Forest.
Forestry Commission has put up notices around the New Forest to warn dog walkers. Walker advised dog owners to be 'vigilant' and take immediate help from vets if lesions appear on their pet's skin.