New WNV Cases in California, EEE Cases in Wisconsin

Seven horses in California have been confirmed positive for West Nile virus (WNV) so far in 2011, according to a statement from the California Department of Food and Agriculture (CDFA). One of the seven was euthanized as a result of the disease, the statement said, while the other six animals are recovering.

The statement reported that the affected animals are located in the following counties: Fresno (two confirmed cases), Kern, Los Angeles, Placer, Merced, and Tulare. The report did not note if the WNV-positive horses had been vaccinated against the disease.

"The CDFA continually monitors and investigates equine neurological cases for the presence of WNV in California," the statement said. "The CDFA urges horse owners to consult their veterinarian on a vaccination program to ensure maximum protection of their horses."

In 2010 the USDA's National Animal Health Surveillance System reported 125 confirmed WNV cases in 28 states. Clinical signs for WNV include flulike conditions 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%.

Further, an International Society for Infectious Diseases alert indicated a horse residing in Clark County, Wisc., tested positive for Eastern equine encephalitis (EEE).

Last month in Wisconsin, horses in Price and Taylor counties were confirmed as EEE-positive, and a horse in Clark County tested positive for WNV.

The virus, which is transmitted to horses through mosquito bite and affects the central nervous system, is fatal to horses in 75-95% of the cases. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care. Horses that survive might have long-lasting impairments and neurologic problems.

Clinical signs for EEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures.

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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