The Seaham case is one of nine to be confirmed nationwide and is the first in this region for 20 months.
Further details have still to be announced other than the dog is believed contracted the illness – a flesh-eating bug which attacks blood vessels and kidneys – while being walked in the area in January.
David Walker, the country’s leading expert on the condition, who works for the Anderson Moores specialist referral centre for cats and dogs, near Winchester, said there was no known way of preventing dogs from contracting the illness.
He added: “We are sad to announce more cases from this year, as we are now in the time of year when cases are most common.
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“Further confirmed cases mean it is understandably very worrying for dog owners.
“However, this disease is still very rare, so we’re advising dog owners to remain calm, but vigilant and seek advice from their local vet if their dog develops unexplained skin lesions.”
The disease gained its name after it was first observed among greyhounds in the American state of Alabama in the 1980s.
The first UK case was confirmed eight years ago and it is now known to affect all different kinds of breeds, regardless of age, sex or weight.
Tell tale signs include swellings, patches of red skin and open ulcer-like wounds, usually found beneath knees or elbows.
Dr Huw Stacey, of Vets4Pets, part of the nationwide Pets At Home Vet Group, has been supporting research for a number of years and is advising dog owners to contact their vet if they have any concerns.
He said: “While it is understandable that dog owners will be worried by Alabama Rot, it is still a very rare disease and we’d encourage owners to continue exercising their pet.
“If a dog becomes affected, the best chance of recovery lies with early and intensive veterinary care at a specialist facility such as Anderson Moores.
“Treatment is supportive, but is only successful in around 20% of cases.”