Oklahoma State Health Officials Warn of WNV Resurgence

State health officials in Oklahoma are warning residents and horse owners to protect themselves and their horses against the mosquito-borne West Nile virus (WNV), according to a news release from the Oklahoma State University College of Veterinary Medicine.

"Surveillance indicators so far this year suggest that we are on track for a more severe WNV season," the release read. "This summer and fall we need to take mosquitoes more seriously."

According to the USDA Animal and Plant Health Inspection Service National Animal Health Surveillance System, 87 cases of WNV were detected nationwide in 2011; no cases were confirmed in Oklahoma. Oklahoma's last confirmed WNV case came in Sept. 2009 when a horse from Cherokee County tested positive for the disease.

First confirmed in the United States' horse population in 1999, WNV infection is responsible for equine clinical signs including flulike signs, 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%.

Horse owners can take several steps to protect their charges from contracting WNV, one of which is vaccination against the disease. The American Association of Equine Practitioners (AAEP) considers the WNV inoculation a core vaccine and recommends horses be vaccinated annually. The AAEP's complete WNV vaccination guidelines are available online.

Other preventive measures include reducing horses' exposure to mosquitoes by:

  • Reducing or eliminating stagnant or standing water sources, which can serve as mosquito breeding grounds;
  • Removing manure from areas near the horses;
  • Stabling horses during peak mosquito periods (i.e., dawn and dusk);
  • Using equine-approved mosquito repellants; if additional protection is desired, consider using fly masks, sheets, and/or leg wraps;
  • Placing fans inside the barns or stalls to maintain air movement as mosquitoes don't fly well in wind;
  • Avoiding use of incandescent blubs inside stables at night, which attract mosquitoes; and
  • Discouraging wild birds--which can harbor WNV--from roosting near or in your stables.

If a horse is suspected of having WNV, contact a veterinarian immediately to begin treatment.

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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