Pet owners are being warned not to let their dogs drink or swim in streams after a spate of deaths from a disease caused by bacteria often carried by rats. Ten dogs out of at least 12 that have fallen ill in recent weeks with leptospirosis - a water-borne disease also potentially fatal to humans - have died. One remains seriously ill in a veterinary hospital after undergoing a blood transfusion. Many of those infected became ill after walks around The Peak, Pok Fu Lam and Sai Kung. The threat is regarded as so serious that an animal parade and picnic organised as part of Hong Kong's gay and lesbian Pink Season has been postponed after it was revealed that several of the dogs infected with the bacteria had swam in or drunk from streams close to the venue. The Pink Paws Parade was due to take place at the Victoria Peak Gardens next Saturday to coincide with Peace One Day, but its organisers say they have been forced to put it on hold because of fears that the bacteria that causes leptospirosis was in streams near the park. Dr Tony Matthews, who has treated several of the infected dogs at the Acorn Veterinary Hospital in Mid-Levels, said even dogs vaccinated against the disease were falling ill. "About three years ago, we saw three or four cases in summer. Last year we saw over 20, and around 75 per cent we successfully treated," he said. "This year we have already seen five, with a burst of them in the past month. The worrying thing is this year the mortality rate is very high. We are seeing vaccinated dogs with leptospirosis, suggesting it is a new strain." Vet Jonathan Williams, of the Valley Veterinary Centre in Happy Valley, said he had seen at least four dogs over the summer with leptospirosis and all had died. "It is a nightmare, a very nasty disease that can happen to any dog," Williams said. "It comes on very quickly and I would say around 95 per cent of dogs that are infected will die. Those that survive are left with chronic kidney disease and are on medicine for the rest of their lives. "We have seen at least four cases this summer and my vet friends all over Hong Kong are seeing exactly the same as well." The disease is caused by the bacteria leptospira, found in the warm or muddy water in streams, soil or any water where rats may be present, such as puddles. The bacteria enters the body through a cut, via the nose, eyes or mouth, or from contact with the urine of an infected animal. Symptoms in humans include high fever, headache, muscle pain, vomiting and jaundice. An infected dog will display similar symptoms, with a loss of appetite, dehydration and no urination. If untreated, the disease can lead to kidney damage, liver failure, respiratory distress and death in humans and animals. Williams said two vaccinations were available but they covered only four strains and not the one affecting dogs locally. "The worry is owners will have this false sense of security if their dog is vaccinated," he said. "But the Hong Kong strain is one of the nastier types and there is nothing people can do vaccinate their dogs against it. The only thing they can do is keep them out of the dirty water areas." The Department of Health's Centre for Health Protection and the Agriculture, Fisheries and Conservation Department yesterday said they had not received any reports of leptospirosis.