West Nile Virus has been confirmed in three horses in Washington State — the first cases in the state this year.

Last year Washington State had the highest number of West Nile Virus cases in the US, with 41 horses testing positive for the disease.

On Friday (31 July) the Washington Animal Disease Diagnostic Laboratory and the state Department of Agriculture confirmed one-year-old gelding quarter horse in Kittitas county had the disease. It was put down.

And at the end of last month (24 July) West Nile Virus was confimed in two other horses in the state.

An eight-year-old quarter horse mare in foal in Toppenish was euthanised, while a nine-year-old quarter horse gelding in Prosser is expected to recover.

None of the horses had been vaccinated against the disease.

Meanwhile also this week a horse near Hermiston in Oregon was the first to test positive to the virus in the state this year.

West Nile Virus is spread by mosquitos and can cause neurological damage and death in horses and humans.