A 13-year-old Standardbred mare in Salem County has been identified as the second case of Eastern Equine Encephalitis (EEE), a serious mosquito-borne illness in horses, in New Jersey for 2023.

The horse’s vaccination status is uncertain. The mare was humanely euthanized on Oct. 13, 2023.

There had been one other reported horse case of EEE in New Jersey in Gloucester County in September.

EEE causes inflammation of the brain tissue and has a significantly higher risk of death in horses than West Nile Virus (WNV) infection. West Nile Virus is a viral disease that affects a horse’s neurological system. The diseases are transmitted by a mosquito bite. The virus cycles between birds and mosquitoes with horses and humans being incidental hosts. EEE infections in horses are not a significant risk factor for human infection because horses (like humans) are "dead-end" hosts for the virus.

In general, most regions in New Jersey have a reported mosquito population near the five-year average. The first EEE positive mosquito pool was detected in Gloucester County this year. Livestock owners are strongly encouraged to vaccinate against WNV, EEE and other mosquito-borne diseases. Effective equine vaccines for EEE and WNV are available commercially. Horse owners should contact their veterinarians if their horses are not up to date on their vaccinations against both EEE and WNV.

“We continue to encourage horse owners to be vigilant in vaccinating their animals against these diseases spread by mosquitoes,” said Joseph Atchison III, New Jersey Assistant Secretary of Agriculture. “Vaccinated animals are much less likely to contract deadly diseases such as EEE and West Nile Virus.”

For more information about EEE in horses, visit the New Jersey Department of Agriculture website by clicking here.

EEE and West Nile Virus, like other viral diseases affecting a horse’s neurological system, 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 – [email protected]. Learn more about the NJ Animal Health Diagnostic lab at jerseyvetlab.nj.gov. 

(New Jersey Department of Agriculture)