Grimes, Co., Texas Horse Tests Positive for WNV

Grimes, Co., Texas Horse Tests Positive for WNV

Study results have shown that the WNV vaccine has a substantial effect on preventing disease.

Photo: Erica Larson, News Editor

One horse in Grimes County, Texas, has tested positive for West Nile virus (WNV), according to the Texas Department of State Health Services WNV surveillance program. As indicated on the U.S. Geological Survey WNV disease map, last updated June 18 at 3 a.m., the Grimes County case is the first equine WNV case reported in the United States this year.

The USDA Animal and Plant Health Inspection Service (APHIS) reported 627 equine WNV cases nationwide in 2012, the highest total since 2006, when veterinarians reported 1,086 equine cases. Texas reported the most cases last year (120), followed by Louisiana (62), Pennsylvania (47), and Oklahoma (42). Indiana, Mississippi, and Iowa each confirmed 30 or more equine WNV cases in 2012, according to APHIS. Only nine states—Alaska, Delaware, Hawaii, Kansas, Maine, New Hampshire, Rhode Island, Vermont, and West Virginia—remained equine WNV-free in 2012.

Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculation (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). Equine mortality rate can be as high as 30-40%.

Study results have shown that the WNV vaccine has a substantial effect on preventing disease. The American Association of Equine Practitioners (AAEP) recommends vaccinating all foals and horses against WNV. For horses residing in the northern United States veterinarians recommend vaccinating in the spring prior to peak mosquito levels. In the south, where mosquito populations are present year-round, horses might be vaccinated more frequently. In addition to geography, age and exposure play an important role in deciding how often to vaccinate horses. The AAEP's complete vaccination guidelines are available online.

Additionally, owners are advised to take steps to reduce horses' exposure to mosquitoes:

  • Reduce or eliminate sources of stagnant or standing water, which are prime mosquito breeding grounds;
  • Remove muck from areas near horses;
  • Stall horses during peak mosquito periods (i.e., dawn and dusk);
  • Use equine-approved mosquito repellants and/or protective gear such as fly sheets, masks, and leg wraps;
  • Place fans inside barns or stalls to maintain air movement, as mosquitoes cannot fly well in wind; and
  • Avoid using incandescent bulbs inside stables at night. Instead, place incandescent bulbs away from the stables to attract the mosquitoes to outside areas.

Work with a veterinarian to ensure horses are properly vaccinated against WNV. Contact a veterinarian if a horse exhibits clinical signs consistent with WNV, as early diagnosis and treatment often leads to better outcomes.

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