The first case of equine West Nile virus in Island County was confirmed last week on central Whidbey Island.

A 14-year-old horse became ill with the disease in October. According to the Mount Vernon veterinarian office where it was treated, the horse is recovering and is back home.

The infection came on after the horse received a two-shot vaccination on Sept. 4 and Oct. 2. The animal became ill 10 days later, indicating that a mosquito bit it before immunity was established.

This is the first case of West Nile virus found in a Washington horse.

Oak Harbor veterinarian Kent Freer, who has been vaccinating horses against the disease for several months, said the fact that the horse had received two of the three vaccinations probably contributed to its recovery. He said it takes about 10 days for an animal to develop immunity after vaccination.

Before the horse was diagnosed with the disease, Freer and fellow vet Robert Moody had vaccinated about 300 horses on the island. Freer says he is getting more calls now since the latest news.

They are recommending to all their clients whose horses have had the first shot to get a second vaccination this winter and plan on the third in mid-March.

“Mosquito season should be basically over now, but we can’t predict whether it will be a warm winter and early spring,” Freer said.

The test results on the Island County horse were reported by the Washington Animal Disease Diagnostic Laboratory in Pullman and confirmed on Nov. 13 by the National Veterinary Services Laboratory in Ames, Iowa.

West Nile virus is spread by the bite of an infected mosquito and can infect people, horses, and many types of birds. About one-third of horses that become ill die.

Freer advises older and young horses should be vaccinated.