A 7-year-old horse in Monmouth County, New Jersey has tested positive for Eastern equine encephalitis (EEE). This is the third confirmed case of EEE in New Jersey horses this year.

The horse had not been vaccinated against EEE in 2018 and was euthanized on Sept. 4.

“This is another sad and unfortunate reminder that 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 (WNV).”

The other two cases in 2018 occurred in August and were in Monmouth and Camden counties. Both of those horses had to be euthanized, as well.

In 2017, officials confirmed six cases of EEE in New Jersey horses.

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 be effective EEE prevention tools. Horses vaccinated in past years need an annual booster shot, but veterinarians might recommend two boosters annually—one in the spring and another in the fall—in areas with prolonged mosquito seasons. In contrast, previously unvaccinated horses require a two-shot vaccination series in a three- to six-week period. Full 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: