Unseasonably warm February weather in California is renewing the threat of West Nile virus, which serves as a reminder to horse owners to make sure their animals are vaccinated.

Last year, 456 horses in California were known to have contracted the disease, with 200 deaths. In the great majority of those cases the horses were either not vaccinated or vaccinated improperly.

"Outbreaks of West Nile virus are expected to continue this year," said California State Veterinarian Dr. Richard Breitmeyer. "Horse owners should contact their veterinarians as soon as possible to ensure current vaccination status, so that horses will have maximum protection against the disease."

Signs of West Nile virus include stumbling, staggering, wobbling, weakness, muscle twitching and inability to stand. Horses contract the disease from carrier mosquitoes and are not contagious to other horses or people. Not every horse exposed to the virus will die.