West Nile Virus took a toll on the equine population in California last year. Of the 540 horses that contracted the virus, 229 died.
Health officials say West Nile has already been detected in birds in the state this year and it's just a matter of time before it spreads.
Steve Lyle, of the California Department of Food and Agriculture says horse fatalities could increase. "Many health care professionals believe that this year could be worst than last year."
Last year officials estimated that only one half of the state's six hundred thousand horses were immunized for West Nile. Jan Hannick, a horse trainer from Modesto says the number of deaths last year has had a sobering affect on owners. "I don't know of very many people that would resist doing the immunization at this point."
There are two shots that make up the vaccination. Veterinarians emphasize that the second one is just as critical as the first.
Vets say any horse that hasn't received the first shot should get one immediately.
There is no immunization for humans.