Eastern Equine Encephalitis

EEE in Alachua County

Information provided by Dr. Robert MacKay, Veterinarian of UF Large Animal Internal Medicine, Professor, DACVIM, PhD, BVSc (Dist).

What is Eastern Equine Encephalitis?

Eastern Equine Encephalitis is a viral disease caused by infected mosquitoes. When an EEE-infected mosquito bites a non-immune horse (or human), the virus spreads through the body and attacks the central nervous system (brain and spinal cord) causing nervous signs such as profound depression, blindness, staggering and even seizures. Most affected horses die within several days. All horses are at risk although young adults (six months to two years) are particularly vulnerable.

Can an infected horse spread the disease?

No. EEE is only spread via mosquitoes that have previously fed on infected birds. Horses do not have enough virus in their system to infect mosquitoes themselves, even when in the throes of EEE. The virus also is not spread by direct contact between horses.

What can I do to prevent Eastern Equine Encephalitis?

  • Large fan in barn
    Vaccinate your horses for EEE at least twice yearly. This is BY FAR the most important step you can take to prevent this fatal disease. Vaccination of foals begins at 6 months of age if their dams have been vaccinated, or 3 months if they have not. Your veterinarian is your best resource for detailed information on correct vaccination schedules for your area.
  • Remove sources of standing water in pastures on your property.
  • Apply fly masks, fly sheets and/or fly leggings to horses when they are at pasture.
  • Spray horses with insect repellent. Regular fly sprays work but only for a few minutes. Longer-acting oil-based repellents are available through your feed store or veterinarian.
  • Keep horses inside during the hours around dawn and dusk. These are the peak feeding times for mosquitoes.
  • Turn fans on in barns for stalled animals or open barn windows to create a breeze. The more powerful the fan, the better the protection.
  • Don’t forget to protect yourself by using insect repellent or wearing protective clothing.

What are signs of EEE in horses?

  • High fever (temperature higher than 103 F)
  • Dullness, depression, lack of appetite
  • Walking aimlessly, often in circles
  • Pressing the head into corners
  • Blindness
  • Staggering, uncoordinated gait
  • Recumbency
  • Seizures
  • Death (in more than 80% of cases)

Other mosquito-borne illnesses

What if my horse becomes infected with EEE?

If you suspect your horse might have EEE, call your veterinarian or contact the UF Large Animal Hospital immediately. EEE infection can be confirmed by a blood test that takes 2 to 5 days from submission to reporting. Treatment is limited but centers on making affected horses as comfortable as possible.

More Information

The UF Large Animal Hospital veterinarians treat equine and large animal patients from the Gainesville, Ocala and Jacksonville areas, including Alachua and Marion Counties in Florida, and our clients come from all over the United States. Contact us to make an appointment.

University of Florida


As part of both the Institute of Food and Agricultural Sciences and UF Health, Veterinary Medicine is dedicated to advancing animal, human and environmental health through teaching, research, extension and patient care.

IFAS footerblock

University of Florida

Animal Hospitals

Need animal care? Visit the UF Small Animal and Large Animal Hospitals. From dogs, cats, birds and exotics to horses, cattle, llamas, pigs and many other large farm or food animals, our experienced veterinary staff is ready to assist.


Syndicated Podcast

Animal Airwaves

Animal Airwaves is a daily radio series that features one-minute segments relating to animal health, ranging from insights into animal behavior to veterinary patient care breakthroughs and trends.