Vashon veterinarian Dana Ness said she has seen at least three confirmed cases of dogs with leptospirosis this winter, raising concerns that the sometimes fatal disease could be coming back to the Island.

She and her colleagues at Fair Isle Animal Clinic have seen another seven cases that could be the bacterial disease. Vashon experienced an outbreak of leptospirosis a few years ago, Ness said. She and others are carefully monitoring the situation to determine if the disease is returning to Vashon.

But diagnosis is tricky, she added, and treatment is best if it occurs right away.

“It presents as such a nebulous thing,” she said.

Symptoms in dogs include vomiting, lethargy, depression, muscle pain and sometimes diarrhea. The disease is spread in the urine of infected animals, such as raccoons, as well as in ponds and puddles.

A vaccine exists for the disease, though it’s not yet clear if it covers the strain that’s now on Vashon. Ness encourages pet owners to contact their veterinarian if they believe their dog is ill.

“I think it’s going to be an issue this winter with our warmer weather,” Ness said.