New Equine EEE, WNV Cases Confirmed Across Country

New Equine EEE, WNV Cases Confirmed Across Country

Summer might be winding down in some areas of the country, but the number of equine mosquito-borne disease cases continues to rise.


Summer might be winding down in some areas of the country, but the number of equine mosquito-borne disease cases continues to rise. Animal health officials in California, Kentucky, and Vermont have all issued statements regarding newly confirmed cases of either Eastern equine encephalitis (EEE) or West Nile virus (WNV) in the past week.

The USDA Animal and Plant Health Inspection Service (APHIS) reported 87 cases of WNV and 60 cases of EEE in U.S. horses in 2011. As of Sept. 4, APHIS has reported 181 cases of WNV and 112 cases of EEE throughout the nation.

California--The California Department of Food and Agriculture (CDFA) yesterday (Sept. 17) announced that five additional WNV cases were confirmed in three counties.

"The CDFA Animal Health Branch confirmed five additional cases of WNV ... in Calaveras, Kern, and Shasta counties," a statement read. "All five horses were unvaccinated. One of the five horses was euthanized."

The CDFA reports that 16 California horses in 11 counties--Butte, Calaveras, Fresno (2), Glenn, Kern, Merced, Sacramento (2), San Joaquin (2), Shasta (3), Stanislaus, and Yolo--have now tested positive for WNV in 2012. Five of the 16 have been euthanized.

Kentucky--In Kentucky, Equine Programs Manager E.S. "Rusty" Ford announced Sept. 13 that a yearling Standardbred filly from Bourbon County had tested positive for WNV. The filly is the second WNV-positive horse in Bourbon County this year.

Ford said the filly is responding well to treatment. He noted that the "farm's population received 2012 WNV vaccines around Aug. 30; younger stock with no vaccination history have a vaccine booster pending."

Kentucky has confirmed 11 WNV cases on 10 premises in nine counties (Bourbon, Franklin, Henderson, Henry, Laurel, Metcalfe, Scott, Shelby, and Warren) so far this year. Six are recovering while five have been euthanized. Ford reported that seven affected horses were unvaccinated, three were partially vaccinated, and one was reportedly vaccinated.

Vermont--Finally, Vermont animal health officials confirmed Friday (Sept. 14) the state's first-ever case of EEE.

"The Vermont Agency of Agriculture, Food, and Markets was notified on Sept. 14 that a horse located in Whiting has tested positive for EEE," a news release stated. "The horse was not vaccinated for EEE. This case represents the first time that a horse has tested positive for EEE in Vermont."

The state has not reported any equine WNV cases this year.

Clinical signs for WNV include flulike 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. Equine mortality rate can be as high as 30-40%.

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. Its fatality rate in horses is 75-95%. 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 of 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.

Vaccinations are available for both diseases, and the American Association of Equine Practitioners recommends all horses receive both annually.

Horses with clinical signs of WNV or EEE should be evaluated by a veterinarian immediately.

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.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More