West Nile, EIA Confirmed in Tennessee Horses

West Nile, EIA Confirmed in Tennessee Horses

West Nile is transmitted to horses via bites from infected mosquitoes.

Photo: Thinkstock

The Tennessee state veterinarian has announced that two horses in that state have tested positive West Nile virus (WNV) and one has been confirmed positive for equine infectious anemia (EIA).

The WNV-positive horses are located in Davidson County and Knox County, and the EIA-positive horse was identified in Bedford County.

“We think about the summer as being bad for biting insects, but the risk carries well into the fall,” State Veterinarian Charles Hatcher, DVM, said in an Oct. 6 statement. “Horse owners need to be vigilant, take preventive measures, and practice good animal husbandry to protect their livestock year-round.”

West Nile is transmitted to horses via bites from infected mosquitoes. Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculation; 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. There are no specific treatments for WNV, however supportive care can help horses recover in some cases. Equine mortality rate can be as high as 30-40%.

Health Alert: West Nile Virus

West Nile vaccines have proven to be a very effective prevention tool. Horses that have been vaccinated in past years will need an annual booster shot; in areas with a prolonged mosquito season, veterinarians might recommend two boosters annually—one in the spring and another in the fall. However, if an owner did not vaccinate their animal in previous years, the horse will need the two-shot vaccination series within a three- to six-week period.

In addition to vaccinations, horse owners also need to reduce the mosquito populations and their possible breeding areas. Recommendations include removing stagnant water sources, keeping animals inside during the bugs’ feeding times, which are typically early in the morning and evening, and applying mosquito repellents approved for equine use.

Equine infectious anemia is a viral disease that attacks horses' immune systems. The virus is transmitted through the exchange of body fluids from an infected to a noninfected animal, often by blood-feeding insects such as horseflies or through the use of blood-contaminated instruments or needles.

There are typically a small number of cases of EIA in the United States every year, although the disease is common in other parts of the world. The disease is controlled in the United States by regular testing before traveling across state lines and/or exhibition. A Coggins test screens horses' blood for antibodies that are indicative of the presence of EIA.

Once an animal is infected with EIA, it is infected for life and can be a reservoir for the spread of disease. Obvious clinical signs of the disease include progressive loss of condition along with muscle weakness and poor stamina. An affected horse also could show fever, depression, colic, swelling, or anemia.

In the statement Hatcher advised horse owners to consult with their veterinarians to establish a schedule for vaccines and Coggins tests. 

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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