Vaccination, Mosquito Reduction Can Help Prevent
West Nile Virus in Horses

In addition to warmer temperatures and longer days, summer also brings the onset of mosquito season and an increased chance of your horse being exposed to West Nile virus (WNV).

“WNV tends to be more prevalent in the late summer and early fall, despite where you are in the country,” says Dr. Judith Marteniuk, equine extension veterinarian, Michigan State University. “In the Southern states, we see a year-round mosquito season, but the most common time to see West Nile is still in the late summer and early fall.”

WNV can be fatal to both horses and humans. Transmitted by mosquitoes, it causes swelling of the brain. Once infected, horses may present a wide range of clinical signs, including fever, depression, muscle tremors, weakness, lack of coordination and paralysis.1 About one in every three horses showing clinical signs of WNV dies. About 40 percent of surviving horses show residual effects, such as gait and behavioral abnormalities, for up to six months after diagnosis.

“Horses of all ages, breeds and in all areas of the United States can be infected with WNV,” says Dr. Frank Hurtig, DVM, MBA, director, Veterinary Services, Merial. “That’s why the American Association of Equine Practitioners (AAEP) revised its core vaccination guidelines to include WNV.4 It is a disease that all horse owners should be concerned about.”

WNV was first diagnosed in the eastern United States in 1999, but is now considered to be endemic to all areas,3 putting horses in every part of the country at risk of being exposed. Additionally, there is no specific treatment for horses once they have been infected with WNV.5

“The only thing to do is provide the best supportive care possible,” Dr. Marteniuk says. “Keep the horse quiet, in a nonstressful environment and provide nutritional support. Depending on severity, some horses may need intravenous feedings or a stomach tube. It’s also important to control fever and inflammation as much as possible.”

Treatment for WNV infections can be costly. While there are ways horse owners can reduce the threat of WNV, the best way to prevent it is with regular vaccination.3 WNV vaccinations typically protect horses for nearly an entire year, but in some parts of the United States, horses may require an additional booster to ensure they are protected for the duration of the mosquito season.3

“Even though WNV vaccines provide almost a full year of protection, many veterinarians recommend multiple boosters,” Dr. Marteniuk says. “Horses living in the southern part of the country are especially likely to need at least one booster.”

Horses that travel into a mosquito area or south in the winter for training, competition or racing also should receive boosters, Dr. Marteniuk adds. Because of the extended mosquito season in warmer locales, performance horses have an additional risk of exposure to WNV.3  

“Vaccination is the best way to prevent West Nile,” Dr. Marteniuk says. “WNV vaccines actually have a good vaccination protection rate. But, it’s still important to work with a veterinarian to create the right vaccination program for your horse.”

Horse owners should choose a vaccine that will start working fast and will help guard against WNV for the duration of the mosquito season, like RECOMBITEK® Equine WNV vaccine from Merial.6 RECOMBITEK is proven to protect horses fast — just 14 days after the initial two-dose vaccination series6 — and is safe for foals at least 2 months old. 7

“Even though WNV tends to be more prevalent during late summer and early fall, it’s important to remember WNV can strike at any time throughout the summer months, and booster vaccinations will help keep your horse protected as mosquitoes linger,” Dr. Hurtig adds.

In addition to vaccination, Dr. Marteniuk recommends several simple ways horse owners can reduce the risk of WNV, including minimizing the mosquito population on their property by removing any items that may collect water or dew.2

“Make sure you don’t have old tires or buckets collecting water,” Dr. Marteniuk says. “Try to keep your horses in the barn at dawn and dusk and provide a fan to keep air moving. Using barriers like blankets, leg wraps and bug spray also may help.”

When concentrating on your horse, owners shouldn’t forget to take care of themselves, too. With no human vaccine, horse owners should take precautions by using bug spray, and wearing long sleeves and pants at peak mosquito times, Dr. Marteniuk adds. Despite a recent downturn in the number of documented WNV cases, 8 it’s important for people to continually consider the threat of WNV.

“It’s important that people don’t become complacent about caring for themselves and vaccinating their horses,” Dr. Marteniuk says. “Just because WNV isn’t in the news doesn’t mean that the conditions aren’t right to have a large number of cases of WNV again. WNV is one of the diseases that needs to be on our radar — it is one of the vaccines that needs to be in every vaccination program.”

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