CHEYENNE, Wyo. (AP) — Despite the onset of fall, cases of West Nile Virus in horses continue to be reported throughout the state of Wyoming.

At least 15 West Nile horse cases have been diagnosed this season by the Wyoming State Veterinary Laboratory.

State Veterinarian Jim Logan says the West Nile season can last until a hard frost.

The Wyoming Livestock Board veterinary staff recommends that owners vaccinate their horses if they have not done so already.

Horses are far more affected by the West Nile than other livestock and domestic animals. Signs of West Nile include initial flu-like symptoms, where the horse becomes lethargic and depressed, followed by weakness and seizures.

Of those that become ill, about 30 percent die or need to be euthanized.