West Nile virus and Eastern Equine Encephalitis: How to protect humans and horses alike

by Hillary on September 27, 2012

Horse and rider aerating a body of water to prevent mosquito larvae. Probably best to use a circulation pump, though.

This year has been a big year for West Nile virus (WNV) and Eastern Equine Encephalitis (EEE) infection, two mosquito-borne diseases that can cause severe neurological disease in humans and equines. For example, Massachusetts health officials recently confirmed its second human EEE death and seventh case this year. For comparison, the CDC states that there is an average of six cases of EEE a year in the United States. In regards to West Nile, The CDC reports that this year has seen the highest number of cases since 2003 and 147 reported deaths.

First, a little bit about the diseases – both are viral infections that can cause encephalitis (swelling in the brain). WNV can present with symptoms including, but not limited to, disorientation, high fever, and stiff neck in humans and hind limb weakness, hind limb paralysis, and fever in horses. Case fatality in horses is estimated to be 33%. EEE can also present with multiple symptoms. In humans, those can include fever, convulsions, and vomiting/diarrhea. In horses, the infection can present with fever and a lack of coordination.

Humans can avoid infection by reducing how frequently mosquitoes bite. This can be accomplished by removing mosquito breeding areas in the environment (be it home, yard, or barn) or by protecting yourself against bites. Since horses are frequently outside for turnout and barns are typically not sealed in such a way as to keep out mosquitoes, the best method to protect horses is to get them vaccinated yearly.


  • Fix screens in windows and doors.
  • Wear repellant and long sleeves/pants.
  • Avoid being outside when mosquitoes are active (dusk and dawn, primarily).
  • Remove sources of stagnant water (where mosquitoes breed). You can add circulators to bird baths or fountains to larger standing bodies of water. Make sure that any standing water in buckets, tires, ect gets dumped.
  • Vaccinate horses yearly for WNV and EEE. Check with your veterinarian to make sure all horses are up to date on vaccines.

Even if you take precautionary measures, it’s still possible to meet the wrong mosquito at the wrong time. If you or your horse gets sick, please call your physician/veterinarian!

Information sources: