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News Release

California Department of Food and Agriculture

Media Contact: Steve Lyle, Office of Public Affairs, (916) 654-0462,

California Department of Food and Agriculture
Release #05-019
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Earlier start of season compared to 2004

SACRAMENTO - The first positive equine case of West Nile Virus (WNV) in California in 2005 has been reported in Plumas County. The horse, which is recovering, is a 3-year-old quarter horse mare. The case was confirmed about a month earlier than the first case of 2004. 

WNV is a mosquito–borne virus that was first detected in the United States in 1999 in the New York City area. It may cause a wide range of clinical illnesses from mild, “flu-like” symptoms to encephalitis (inflammation of the brain) that may be fatal to both humans and horses. While horses are susceptible to WNV, many horses infected with the disease will not develop any illness and will recover uneventfully. Currently, there is no specific treatment for WNV.

California became the focus for West Nile Virus in 2004 with 540 confirmed clinical equine cases.  Over 40 percent of clinically affected horses died or were euthanized. In 2004, WNV was detected in all California counties. The Centers for Disease Control has predicted that California will again be the epicenter for WNV in 2005.

Signs of West Nile Virus in horses include stumbling, staggering, loss of coordination, muscle twitching, circling, and inability to stand. Birds serve as the primary reservoir for harboring the disease. Mosquitoes transmit the disease to humans and horses after feeding on infected birds. Once infected, horses do not spread the disease to other humans or horses.

The California Department of Food and Agriculture is urging horse owners to consult their veterinarian to ensure each horse is current on West Nile Virus vaccinations. It is also important to practice mosquito control methods to aid in reducing mosquito-breeding sites.

For more information on West Nile Virus in horses, call the Equine West Nile information line 1-800-268-7378 or email or visit


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California Department of Food and Agriculture Office of Public Affairs
1220 N St., Ste. 214, Sacramento, CA 95814