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Recommended Vaccines for Equine Encephalomyelitis

As a horse owner, it is important to understand which diseases pose a threat to your horse’s health. Part of your horse’s health care plan should include vaccination against the core equine diseases, as established by the American Association of Equine Practitioners (AAEP). Two viral diseases which make AAEP’s list include:

  • Eastern Equine Encephalomyelitis (EEE, EEEV, or Triple E)
  • West Equine Encephalomyelitis (WEE or WEEV)

If left unprotected, horses can suffer severe nervous system damage from these diseases.

Equine Encephalomyelitis

Both EEE and WEE are viral infections which spread through the bite of a blood-sucking insect, in this case, the mosquito. Horses cannot spread the virus to other animals or humans.

Geographically, both diseases can be found in North America. EEE is largely found in states located on the East Coast and some northeastern states. WEE has a higher occurrence in states west of the Mississippi River. See our map below for a visual representation of the states most likely to be affected by WEE.

Foals and older horses, as well as those with weakened immune systems, are likelier to contract one of these viruses; however, any horse can contract either virus.

Symptoms and Treatment

Symptoms of Equine Encephalomyelitis can include, (but are not limited to):

  • Fever
  • Staggering
  • Circling
  • Head Pressing
  • Depression
  • Sleepiness

There is currently no known cure for either virus. Treatment is generally supportive.

Horses who contract EEE have a 10-50% chance of survival, while those who contract WEE have a 50-80% chance.

Preventing Equine Encephalitis

Vaccination is the leading preventative method for both diseases. Beyond vaccination, developing an effective mosquito control program can help limit your horse’s risk of exposure. As the saying goes, “the little things can make a big difference.” Some of those little things include:

  • removing standing and stagnant water
  • using an insect repellent that protects against mosquitoes as well as flies
  • keeping horses inside during mosquitoes’ most active hours (dusk and dawn)

While these viruses may never be eradicated, vaccination and mosquito management can significantly decrease the chances of your horse coming into contact with either.

Horse Vaccine FAQs

      1. What Type of Equine Vaccines Are Available? All available vaccines are killed virus vaccines, meaning that the virus is inactive and cannot infect the host.
      2. How is the Vaccination Administered? Intramuscular.
      3. At What Age Should I Begin Vaccination? Vaccinations can begin as early as three months of age.
      4. When Should I Vaccinate? The greatest incidence of these diseases occurs from late summer to early fall. For most, this means vaccinating your horse(s) during April, May, or June. For those in the Deep South, this can be as early as late February or March.
      5. How Often Should I Vaccinate? After the initial series, vaccination should occur annually.

    What About Venezuelan Equine Encephalomyelitis?

    While VEE does not make AAEP’s list of core diseases to vaccinate against, you should still take it into consideration. Largely found in South America, VEE is not an immediate threat to horses in North America. However, outbreaks can and have occurred and the disease has spread to the United States. In the event of an outbreak, Mexico and the Gulf States are at the largest risk of infection. Horses that contract VEE have a low rate of survival.

    Click for a selection of Jeffers’ EEE Vaccines and WEE Vaccines.


    All information in this blog is purely informational. Please consult with your veterinarian to develop a program that works best for your horse’s individual needs.

    Still have questions? Contact Jeffers’ Equine Specialist Kim Cahill. Reach Kim via email at kcahill@jefferspet.com or via phone at 1-800-533-3377.

    Visit JeffersPet for the full selection of equine vaccinations that Jeffers carries.

    For more on protecting your horse from mosquitoes, read “Summer’s Most Deadly Threat to You & Your Horse.