California's Tenth Equine WNV Case of 2012 Confirmed

The California Department of Food and Agriculture (CDFA) confirmed one additional case of equine West Nile virus (WNV) last week, according to a statement on the organization's website.

"On Sept. 4, 2012, the CDFA Animal Health Branch confirmed one additional case of West Nile Virus in an unvaccinated 3-year-old filly located in Butte County," the statement read. "The horse was euthanized."

The Butte County filly is the tenth California horse to test positive for WNV in 2012. The nine other cases were identified in Fresno (2), Glenn, Merced, Sacramento, San Joaquin (2), Stanislaus, and Yolo counties. Three of the positive horses have been euthanized, the CDFA reports.

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 (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 American Association of Equine Practitioners recommends all horses be vaccinated against WNV at least annually and possibly more frequently, depending upon geographic location. Many veterinarians are urging horse owners to ensure their animals' WNV vaccines are up to date, given the rise in case numbers this year. 

The USDA Animal and Plant Health Inspection Service reported 83 cases of WNV in U.S. horses in 2011, with 15 of those cases being identified in California horses.

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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