Two Navajo Nation Horses Test Positive for WNV

Two Navajo Nation Horses Test Positive for WNV

A viral disease, WNV is transmitted to horses by infected mosquitoes.


The Navajo Nation Veterinary and Livestock Program (NNVLP) has confirmed that two horses exhibiting neurologic signs tested positive for West Nile virus (WNV) on July 25.

The affected horses reside on two premises in the St. Michaels and Hunters Point communities in Arizona, a statement from the agency said. Kelly Upshaw-Bia, DVM, NNVLP Tse Bonito clinic veterinarian, submitted the horses' blood for testing, the statement said.

A viral disease, WNV is transmitted to horses by infected mosquitoes. 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%.

Health Alert: West Nile Virus

Studies have shown that the WNV vaccine has a substantial effect on preventing disease. The American Association of Equine Practitioners 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.

In addition to vaccination, owners can reduce horses' mosquito exposure by:

  • Keeping horses indoors during peak periods of mosquito activity at dusk and dawn, if possible;
  • Reducing the use of artificial light when mosquitoes are active;
  • Using fans to help keep mosquitoes off horses while they are stabled;
  • Using topical repellents designed for use on horses and/or protective fly masks, sheets, and boots;
  • Eliminating areas of standing water in such locations as discarded tires, manure storage areas, drainage areas, wheel barrows, pots, and shallow ponds;
  • Cleaning livestock water troughs weekly or adding a supply of mosquito fish, which will feed on mosquito larvae; and
  • Cleaning storm drains and gutters in areas where horses are kept.

"Take precautions for yourselves and your horses, and use DEET products when out doors for people and insecticide spray for horses," the NNVLP statement said. "Should you see any horses with the previously described signs and symptoms or a large number of dead birds or horses in one location, please contact the nearest Navajo Nation Veterinary Clinic."

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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