New Mexico Reports First Equine WNV Case of 2014

New Mexico Reports First Equine WNV Case of 2014

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


State officials are recommending mosquito control measures to protect both humans and horses after lab tests confirmed the state’s first known case of equine West Nile virus (WNV) this year.

The horse, which resided at a property in Albuquerque’s South Valley, had to be euthanized last week after developing West Nile virus. The animal had not been vaccinated against the disease.

The case comes two months into New Mexico’s monsoon season, which has given rise to mosquito populations that can carry West Nile virus and transmit it to horses and human alike.

“Because of the large amounts of rainfall New Mexico received recently, mosquito populations are increasing, and we should expect West Nile virus activity throughout the state,” said Paul Ettestad, DVM, MS, public health veterinarian for the New Mexico Department of Health.

There have been no human cases of West Nile virus infections in New Mexico this year. The state typically sees most of its West Nile virus cases in both humans and horses in August and September.

“West Nile virus remains an important disease in unvaccinated horses,” said New Mexico State Veterinarian Ellen Mary Wilson, DVM. “Annual vaccination of horses for West Nile virus, conscientious mosquito control, application of mosquito repellant, and minimizing horse exposure during peak mosquito feeding periods will all decrease the risk of infection.”

Health Alert: West Nile Virus

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%.

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.
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