Nearly 700 human cases of West Nile virus (WNV) have been confirmed in the United States thus far in 2012, according to a recent statement from the Center for Disease Control (CDC). So it should come as no surprise that many veterinarians are recommending horse owners ensure their animals are properly vaccinated against the potentially deadly mosquito-borne disease.
"The 693 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the second week in August since West Nile virus was first detected in the United States in 1999," the CDC statement said. "Over 80% of the cases have been reported from six states (Texas, Mississippi, Louisiana, Oklahoma, South Dakota, and California) and almost half of all cases have been reported from Texas."
In 2011, 30 U.S. states reported 87 cases of equine WNV, according to the USDA Animal and Plant Health Inspection Service National Animal Health Surveillance System.
So far in 2012, according to the United States Geological Survey's Disease Maps, 77 cases of equine WNV have been reported in the following states, as of Aug. 14: Arizona, California, Colorado, Indiana, Iowa, Kentucky, Louisiana, Michigan, Mississippi, Missouri, New Jersey, New Mexico, North Dakota, Oklahoma, Pennsylvania, South Carolina, South Dakota, Texas, and Wyoming.
Louisiana--which did not report any equine WNV cases last year--has confirmed the most cases so far this year with 21, according to statistics from the Louisiana Department of Health & Hospitals.
Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculation (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%.
Studies have shown that the WNV vaccine has a substantial effect on preventing disease. The American Association of Equine Practitioners (AAEP) 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. The AAEP's complete vaccination guidelines are available online.
Additionally, owners are advised to take steps to reduce horses' exposure to mosquitoes:
- Reduce or eliminate sources of stagnant or standing water, which could be used as mosquito breeding grounds;
- Remove muck from areas near horses;
- Stall horses during peak mosquito periods (i.e., dawn and dusk);
- Use equine-approved mosquito repellants and/or protective horse gear such as fly sheets, masks, and leg wraps;
- Place fans inside the barns or stalls to maintain air movement, as mosquitoes cannot fly well in wind; and
- Avoid using incandescent bulbs inside stables at night. Instead, place incandescent bulbs away from the stables to attract the mosquitoes to areas outside.
Work with a veterinarian to ensure horses are properly vaccinated against WNV. Contact a veterinarian if a horse exhibits clinical signs consistent with WNV, as early diagnosis and treatment often leads to better outcomes.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.