Horse owners - vaccinate against mosquito borne illness

Wisconsin State Farmer

MADISON – The weather in Wisconsin is starting to change from winter to spring reminding us that mosquitoes will be spreading two diseases among horses that can be minimized by vaccination, Eastern equine encephalitis (EEE) and West Nile virus (WNV). Last year Wisconsin had 19 confirmed cases of EEE and seven cases of WNV, but there could have been many more unconfirmed cases.

Horse owners are encouraged to vaccinate horses against two mosquito-borne illness, which can be fatal to horse.

"Until we see our first mosquito, it’s easy to forget about vaccinations against these diseases,” said Dr. Julie McGwin, equine program manager for the Wisconsin Department of Agriculture, Trade and Consumer Protection’s Division of Animal Health. “We’ve seen the sun emerge to warm things up and the mosquito population will multiply before you know it."

Horses require two doses of the vaccinations initially, and then boosters at least annually.

"Work with your veterinarian on your horse’s vaccination program, so you get the best formulation for your horse and advice about additional boosters later in the season," McGwin said.

Both WNV and EEE are caused by viruses transmitted by mosquitoes, and both may cause encephalitis, or inflammation of the brain. Both viruses can be fatal to horses.

Symptoms are similar for both diseases: depression, appetite loss, drooping eyelids and lower lip, fever, weakness, twitching, paralysis or lack of coordination, aimless wandering, circling and blindness.

Neither of the viruses is contagious between horses. While humans may also be infected by both WNV and EEE, it does not pass between people and horses. Mosquitoes carrying the virus from infected birds and biting warm-blooded animals is the only route of transmission.

Besides vaccination, McGwin recommends taking other steps to limit horses' exposure to mosquitoes once the weather warms up:

  • Remove items from surrounding property that could collect stagnant water such as old tires, tin cans, plastic containers.
  • Keep rain gutters clean and draining properly.
  • Clean and chlorinate swimming pools, outdoor saunas and hot tubs, and drain water from pool covers.
  • Turn wading pools and wheelbarrows upside down when not in use. 
  • Empty and replace water in birdbaths at least once a week.
  • Consider keeping horses in the barn from dusk to dawn, when mosquitoes are most active.