A horse in Lea County, N.M., has been confirmed with the West Nile virus, a mosquito-borne illness that also can strike humans.

It was the first case in a horse in New Mexico this year, the state Department of Health said. There have been no human cases this year.

The yearling filly was brought in late last month, so weak it could no longer stand, and was destroyed, said Dr. Mary Cap, a veterinarian with Mountain States Equine in Hobbs. She said the horse had been sick for at least two days.

Cap said there have been fewer cases of West Nile virus in horses, and believes that’s due to the fact many horse owners are vaccinating their animals