TRENTON, N.J. — A 9-year-old Atlantic County mare is the second reported case in 2017 of Eastern Equine Encephalitis (EEE), a serious, mosquito-borne illness in horses. The horse had not been vaccinated against EEE for two years and is undergoing treatment. The onset of the illness was Sept. 17.

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

EEE causes inflammation of the brain tissue and has a significantly higher risk of death in horses than West Nile Virus infection. West Nile virus is a viral disease that affects horses’ neurological system. The diseases are transmitted by mosquito bite. The viruses cycle 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 considered to be "dead-end" hosts for the virus. 

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A 5-year-old Cumberland County mare was the first reported case of EEE in 2017. That horse had not been vaccinated against EEE and died on Aug. 28. 

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

Late summer and early fall are the prime seasons for these diseases. In 2016, four cases of equine EEE occurred in New Jersey between mid-August and mid-September. There were no cases of equine WNV in 2016. For more information about EEE and WNV in horses, click here

EEE and West Nile virus, like other viral diseases affecting horses’ 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 –

Five cases of West Nile reported in New York

According to the Equine Disease Communication Center, the New York State Department of Agriculture and Markets has confirmed five cases of Equine West Nile virus.

An unvaccinated, 19-year-old mare in Clinton County showed an onset of clinical signs which included lethargy, unwillingness to move, muscle tremors and ataxia. The mare was treated for several days but was ultimately euthanized on Sept. 20.

An unvaccinated 13-year-old mare in Livingston County was found in her stall with a swollen muzzle and signs consistent with being cast on Sept. 14. The mare was uncoordinated and reluctant to move upon examination but was still alive at the time of the report.

A 2-year-old colt with no vaccination history in St Lawrence County presented with hind end weakness, was hyper-responsive to stimuli, and muscle tremors in the shoulders on Sept. 12. The outcome of the case is unknown.

An unvaccinated, yearling filly in Erie County showed an onset of clinical signs on Sept. 15 which progressed from off feed to a high fever and neurologic signs including twitching of the head, uncoordinated walk, and tail held off to the side. Despite treatment, the horse continued to decline, went down on Sept. 21 with seizures, and was euthanized the same day.

A yearling filly in Genesee County with no vaccination history showed onset of clinical signs on Sept. 15 which included leaning and unsteadiness. A veterinarian attended the filly on Sept.16.. The owners elected euthanasia.