News Release
California Department of Food and Agriculture
Media Contact:
Steve Lyle, Office of Public Affairs, (916) 654-0462,
Release #03-067
Vaccination and mosquito control essentials for protection
SACRAMENTO – With the recent confirmation of West Nile Virus (WNV) in Arcadia and parts of Riverside County, the California Department of Food and Agriculture is reminding horse owners to be vigilant with horse vaccination and mosquito control.

With the location of several horse racing venues in Southern California, mosquito control remains critical during the fall and winter months.

WNV is spread by mosquitoes that become infected when they feed on infected birds.  Mosquitoes spread the virus to horses through biting.  Infected horses cannot spread the disease to humans or other animals.  To date, there has not been an equine case of WNV originating from California. 

“Horses are susceptible to this virus and vaccination should not be delayed,” said CDFA Secretary William (Bill) J. Lyons, Jr. “Effective mosquito control is also essential to further protect animals.”

People whose horses have already been vaccinated are reminded to consult with their veterinarians about “booster” vaccinations.

While horses are susceptible to the virus, very few horses infected with WNV show any signs of clinical illness.  However, approximately 30 percent of horses that develop clinical signs either die or must be destroyed.  Another 17 percent have been shown to suffer long-term debilitation. 

Clinical signs of WNV include stumbling, a wobbly gait, loss of coordination, inability to stand, circling, hind limb weakness, muscle twitching, convulsions, and paralysis.

CDFA has collaborated with other governmental agencies to prepare for the arrival of WNV in California to minimize the impact of the virus. The agency has taken its public education program directly to the equine community at horse-related events throughout California. CDFA maintains a series of informational items at Any questions about human health impacts should be directed to the state Department of Health Services at (866) 847-2246 or

Facts about WNV

·        Horses infected with WNV are not contagious

·        A mosquito cannot bite an infected horse and re-infect

       another horse or person

·        Horses infected with WNV will not be quarantined

·        Movement restrictions will not be placed on horses

Protect Your Horse

Eliminate mosquito-breeding sites

·        Drain unnecessary standing water (wheelbarrows, tires, etc.)

·        Clean water containers at least weekly, including bird baths and plant saucers

·        Schedule pasture irrigation to minimize standing water

·        Keep swimming pools well chlorinated and drain water from covers

·        Stock water tanks with fish that consume mosquito larvae

·        Stable horses during active mosquito feeding times (dusk/dawn)



Follow CDFA News on Twitter and Facebook
California Department of Food and Agriculture Office of Public Affairs
1220 N St., Ste. 214, Sacramento, CA 95814