Usually spread by rat urine, leptospirosis can lead to liver and kidney failure. It is common for dogs to contract it in Hong Kong during the summer rainy season when splashing through tainted rivers, streams and puddles, or worse, drinking from them. Infected dogs can also spread the disease through their urine.

What makes this year’s outbreak of concern is a low survival rate – about 50 per cent compared with 85 per cent in previous years, according to VDL – and a lack of a vaccine against the new strain, says VDL’s director Dr Fraser Hill.

Hong Kong resident Nicole Schoeni is well aware of the devastating impact of the disease. Last month she, her husband and two girls lost their dog Duchess, a five-year-old Hungarian vizsla, to leptospirosis.

“There have been a few cases recently in south Lantau, so please be vigilant with your four-legged friends … don’t let them drink stagnant water especially around ponds or streams,” she posted on the Hong Kong Dog Owners’ Facebook group.

Five years ago the family’s dog Patch, a Jack Russell cross, now aged nine, survived the disease.

“In Patch’s case, he became noticeably lethargic and was twitching. With Duchess there were no obvious signs until it was too late … she was bright and energetic up to the very end,” Schoeni says.

Dr Josh Steinhaus, internal medicine specialist at the Veterinary Specialty Hospital in Wan Chai, says his clinic has seen a spike in the number of leptospirosis cases: eight so far this year, compared with four last year.

Common symptoms include lethargy, fever, sore muscles, shivering, weakness, increased thirst and urination, vomiting, and runny nose, Steinhaus says. In some cases, an infected animal may not show any symptoms.

“When treated early and aggressively, the chance of survival is increased,” he says. Treatment includes antibiotics and supportive care, and critical cases may require blood transfusions.

Steinhaus says it is important to continue to vaccinate against other strains, since not all the positive tests have been hebdomadis strains.

Vets also echo Schoeni’s plea: keep dogs on a leash around watercourses to prevent them from drinking potentially tainted water.

According to the website of Hong Kong vet service Creature Comforts, in every case of leptospirosis the clinic has seen, the affected dogs had a history of playing in and drinking fresh water from streams.

“Rats live in the bushy areas around The Peak and after heavy rains, their urine will be washed down into streams and waterways around Mid-Levels and Pok Fu Lam. There have also been cases reported in Sai Kung,” the site says.

“Owners are often under the assumption that if the water is running, it is clean and good to drink. However, this is definitely not the case.

“Puppies should be taught not to drink from streams and dogs should be kept on a leash around watercourses if they are prone to drinking and playing in them. Owners should make sure they take drinking water for their dogs during walks so the dogs continue to have access to water.”

Steinhaus urges owners to prevent catching leptospirosis themselves by reducing their exposure to possible sources of the bacteria.

“Avoid contact with dog’s urine, encourage dogs not to urinate in standing water and/or areas where people can get exposed, and wash your hands after handling your pet,” he says.

According to the government’s Centre for Health Protection (CHP), three cases of human leptospirosis have been reported so far this year, in men aged 45 to 67.

Most human infections occur through contact with urine from infected animals, primarily through skin abrasions, open wounds or mucous membranes, and occasionally through eating contaminated food or inhaling the bacteria.

Human to human transfer is rare. The incubation period is usually between four and 19 days.

The CHP said people infected with leptospirosis commonly present with a flu-like illness with high fever, headache, muscle pain, red eyes, sore throat and rash. In some cases, it can cause anaemia and affect the liver, kidneys, lungs and other organs. The disease can be treated effectively with antibiotics.