The disease has no cure and is under-reported. Development of illness is a slow process, possibly making you wonder for days what is wrong with your horse.

West Nile Virus (WNV) is transmitted to horses via bites from infected mosquitoes. Equine mortality rate can be as high as 30-40%. The virus is not contagious and can only pass through the bite of an infected mosquito.

Your horse is at greater risk of contracting WNV if he hasn’t been vaccinated. Vaccines will not protect horses that have already been infected. Check with your veterinarian to see if your vaccinated horse will need a booster.

In addition to vaccinations, there are simple steps you can take to help minimize the mosquito population and breeding areas on your property, thus reducing the risk of contracting WNV.

  • Remove items from your property that could collect stagnant water, such as old tires, plastic containers, and tin cans.

  • Keep rain gutters clean and draining properly.

  • Clean and chlorinate swimming pools, outdoor saunas, hot tubs, and drain the water from pool covers.

  • Turn wading pools and wheelbarrows upside down when not in use.

  • Empty and replace water in birdbaths and troughs frequently.

  • Keep animals inside during the bugs’ feeding times, which are typically early in the morning and of an evening.

  • Use mosquito repellents.

Typical signs and symptoms of WNV can include the following:

  • Flulike symptoms

  • Mildly anorexic and depressed

  • Fine and coarse muscle and skin fasciculation

  • Hypersensitivity to touch and sound

  • Changes in mentality (daydreaming or “not with it”)

  • Occasional drowsiness

  • Propulsive walking (driving/pushing forward often without control)

  • Asymmetrical weakness

  • Asymmetrical or symmetrical ataxia


Visit West Nile Virus In U.S. Horses for a more in-depth look at the silent killer.