California Owners Urged to Vaccinate Horses against WNV

California Owners Urged to Vaccinate Horses against WNV

Horses need to be vaccinated at least annually (sometimes twice annually, depending on their geographic location), ideally prior to mosquito season.

Photo: Kevin Thompson/The Horse

Butte County, California, public health officials are urging horse owners to vaccinate their equids against West Nile virus (WNV) now, if they have not already done so.

Horses are at significant risk for WNV each year, particularly during summer months, and proper vaccination is the best defense. In 2012, 22 California horses were confirmed positive for WNV, and eight of them died or were euthanized. Most of the WNV-positive horses were unvaccinated or improperly vaccinated.

Several effective vaccines are available. Horse owners should discuss vaccination options with their veterinarian to determine an appropriate vaccination plan for their horses. Horses need to be vaccinated at least annually (sometimes twice annually, depending on their geographic location), ideally prior to mosquito season.

In horses, WNV can cause a wide range of clinical signs ranging from mild flulike signs to brain inflammation that can be fatal. Signs of WNV infection in horses can mimic other serious neurologic diseases—including rabies, equine herpes virus, equine protozoal myeloencephalopathy, and Eastern and Western encephalomyelitis—so it's important to consult a veterinarian if a horse exhibits any of the following signs:

  • Stumbling or lack of coordination, especially in rear limbs;
  • Lip drooping or smacking, or teeth grinding;
  • Generalized weakness, muscle twitching, and/or tremors;
  • Head drooping, lethargy, and unresponsiveness;
  • Hypersensitivity to touch or sound;
  • Fever;
  • Difficulty rising or inability to rise; and
  • Convulsions or coma.

Other control measures recommended for decreasing the risk of WNV infection include reducing mosquito populations around your farm by:

  • Eliminating stagnant or standing water by draining ponds, avoiding water overflow from troughs, and reducing irrigation water run-off and pooling;
  • Eliminating accumulated water in flower pot saucers, buckets, and wheelbarrows, and removing old tires and other areas in which water can collect;
  • Stocking ponds, troughs, fountains and other areas of standing water with mosquito fish; and
  • Removing piles of decaying organic matter such as leaves, lawn clippings, and manure

You can also reduce your horses' exposure to potentially infected mosquitoes by:

  • Keeping horses in a barn during peak mosquito feeding hours (dawn and dusk);
  • Using fans to keep air moving in barns and sheds; and
  • Applying mosquito repellents, particularly in the evening.
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