West Nile Virus Confirmed in California, Nevada Horses

The 2011 mosquito-borne disease season continues to affect horse owners across the country. The most recent reports indicate Hthat a horse in California and a horse in Nevada have both tested positive for West Nile virus (WNV).

In 2010, the USDA's National Animal Health Surveillance System reported 125 confirmed cases of WNV in 28 states.

According to the California West Nile Virus Website (produced by the California Department of Public Health, the University of California Davis Center for Vectorborne Diseases, the California Department of Food and Agriculture, and the Mosquito and Vector Control Association of California), a horse in Los Angeles county recently became the first horse in the state to be confirmed WNV-positive in 2011.

Additionally, a horse in Lyon County, Nev., was confirmed WNV-positive by the Nevada Department of Agriculture's Animal Disease and Food Safety Laboratory earlier this week, according to a news report from The Record Courier. In the report, Nevada State Veterinarian Phil LaRussa, DVM, encouraged horse owners to seek vaccination for unvaccinated horses, noting that there are numerous products available for all classes of horses.

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%.

Earlier this year, a Georgia horse tested positive for WNV in late July.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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