Calif. State Veterinarian Recommends Equine WNV Vaccinations

The risk of a return of West Nile virus (WNV) to California this year is renewing calls for horse owners to ensure their animals are vaccinated. In 2011, 15 horses in California were confirmed positive for WNV; four of those 15 were euthanized. None of the euthanized horses were vaccinated against the disease.

"Outbreaks of West Nile virus are still a risk for horses," said California State Veterinarian Annette Whiteford, DVM. "Horse owners should contact their veterinarians as soon as possible to ensure vaccination status is current. If people get the necessary shots for their horses now, the animals will have optimal protection against the disease."

Clinical signs for WNV include flu-like signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations (twitching); hyperesthesia, or hypersensitivity to touch and sound; Changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia (incoordination on one or both sides, respectively). Equine mortality rate can be as high as 30-40%. The USDA Animal and Plant Health Inspection Service reported 83 cases of WNV in U.S. horses in 2011.

The California Department of Food and Agriculture is cooperating with the California Department of Public Health to detect and respond to the disease in California, as horses provide an additional sentinel for disease detection in the environment. For more information, click on

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