PET TALK Managing mosquito-borne diseases in horses

As temperatures warm across the United States, mosquito activity increases, leading to a rise in mosquito-borne diseases for both people and animals.

For horses, this can mean an uptick in rare but deadly conditions like West Nile virus and three forms of equine encephalitis: Eastern, Venezuelan or Western.

Dr. Kallie Hobbs, an assistant professor at the Texas A&M College of Veterinary Medicine and Biomedical Sciences, discusses the threat posed by these diseases as well as how owners can reduce the risk of mosquito-borne diseases by focusing on vaccination and other forms of prevention.

Signs to watch out for

“Mosquitoes tend to like the heat and they tend to like places where there are standing bodies of water,” Hobbs said. “Whenever we think about Texas, Florida and other southern states, mosquitos are, unfortunately, a year-round threat, though they are not as big of a threat in the winter as they are in the summer.”

In the summer, there is often an increase in cases of West Nile virus and of Eastern Equine Encephalitis (EEE), Venezuelan Equine Encephalitis (VEE) and Western Equine Encephalitis (WEE) in horses across the U.S., with the majority of cases occurring in southern states.

For both West Nile virus and other causes of encephalitis, the first symptoms are fever, slow or dull behavior and a lack of appetite. Because encephalitis causes swelling of the brain, it can also lead to neurological signs, including abnormal limb movements and head pressing.

“Unfortunately, mosquito-borne illnesses can be really expensive to treat,” Hobbs said. “Whenever we talk about Eastern Equine Encephalitis virus, it is also commonly fatal.”

If a horse has already lost its ability to stand up by the time it receives veterinary care for any of the mosquito-borne viruses, treatment can often cost up to $20,000.

“Often, you have a horse that’s very alert but doesn’t have the ability to stand,” Hobbs said. “It’s very hard for owners to watch their horses be this sick. Financial implications can also end up being prohibitive for us to be able to treat these patients.”

Stopping the spread

For mosquito-borne diseases, vaccinating greatly reduces a horse’s susceptibility.

“We do recommend that you vaccinate annually for all of the mosquito-borne illnesses in areas where there are higher mosquito populations,” Hobbs said. “Biannual vaccinations can also be helpful.”

The best time to do annual vaccinations is about one month prior to the start of mosquito season, which occurs in early spring for warmer, southern states. A booster vaccine six months later can help protect horses’ health even further.

Beyond vaccination, controlling mosquito populations is the next best way to protect a horse against West Nile virus and other causes of encephalitis. This can include keeping water buckets clean and removing other nearby areas of standing water.

“Some people bathe their horses in vinegar, which can also help with prevention,” Hobbs said. “Flysheets and fly gear are also really helpful for mosquitoes.”

While mosquito-borne diseases can pose a serious threat, owners can vastly reduce their horses’ risk by keeping up to date on vaccinations and through mosquito management. While mosquitos will always be a nuisance, these simple steps can help ensure that they won’t be a real danger to our equine friends.

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Pasture Talk is a service of the College of Veterinary Medicine and Biomedical Sciences, Texas A&M University. Stories can be viewed on the web at vetmed.tamu.edu/news/tag/pasture-talk/. Suggestions for future topics may be directed to [email protected].