First EEE Case for 2019 Confirmed in New Jersey Horse
An approximately 12-year-old mare in Ocean County is this year’s first reported case of Eastern equine encephalitis (EEE), a serious mosquito-borne illness in horses, in New Jersey. The horse had been previously vaccinated against EEE in April and was euthanized on July 23.

“Horse owners need to be vigilant in vaccinating their animals against diseases spread by mosquitoes,” New Jersey Secretary of Agriculture Douglas H. Fisher said. “Vaccinated animals are much less likely to contract deadly diseases such as EEE and West Nile Virus.”

In 2018 New Jersey had five cases of EEE and one case of West Nile virus (WNV), another mosquito-borne neurologic illness.

Effective equine vaccines for EEE and WNV are available. Horse owners should contact their veterinarians if their horses are not already up to date on these vaccinations.

For more information about EEE in horses, visit the New Jersey Department of Agriculture web site at:

Eastern equine encephalitis and WNV, like other viral diseases affecting horses’ neurological systems, must be reported to the state veterinarian at 609/671-6400 within 48 hours of diagnosis. The New Jersey Animal Health Diagnostic Laboratory is available to assist with EEE and WNV testing and can be reached at 609/406-6999 or via email –

EEE 101

A viral disease, EEE affects the central nervous system and is transmitted to equids by infected mosquitoes. Clinical signs in horses include:

  • Moderate to high fever;
  • Depression;
  • Lack of appetite;
  • Cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing);
  • Behavioral changes (aggression, self-mutilation, or drowsiness);
  • Gait abnormalities; and
  • Severe central nervous system signs, such as head-pressing, circling, blindness, and seizures.

The disease can progress rapidly, with death occurring two to three days after onset of clinical signs despite intensive care in some cases. Fatality rates can reach 75-80%. Equids that survive might have long-lasting impairments and neurologic problems.

Studies have shown that vaccines can help significantly reduce the risk of a horse contracting EEE. Horses vaccinated in past years will need an annual booster shot; in areas with a prolonged mosquito season, veterinarians might recommend two boosters annually—one in the spring and another in the fall. Horses unvaccinated in previous years or those with an unknown vaccination history should receive the initial two-shot vaccination series within a three- to six-week period. Immunity takes several weeks to achieve.

In addition to vaccinations, owners should work to reduce the mosquito populations and possible breeding areas and horses’ exposure by: