This is why your horses need to be vaccinated

Mosquito season isn’t over.

A third case of Eastern Equine Encephalitis has been reported in New Jersey, as a 15-year-old Cumberland County mare came up positive and had to be euthanized. Meanwhile, a 10-year-old Salem County stallion is the second case of West Nile Virus (WNV) in 2017 and is being treated. Neither horse had been vaccinated against EEE or WNV.

“We urge horse owners to maintain their vaccination schedules to prevent their animals from getting diseases like these,” said state Secretary of Agriculture Douglas Fisher.

Most veterinarians administer the EEE and WNV vaccines as a combo with tetanus and Western Equine Encephalitis (WEE). EEE has up to a 90 percent mortality rate for horses that have not been vaccinated.

Immunization involves a two-step process for foals or horses that have never been vaccinated, with a booster shot four to six weeks after the initial vaccination. It also is recommended that horses receive an annual booster shot in the spring before mosquitoes are active or before transporting horses to a part of the country where mosquitoes are active year-round.

The first case of WNV in 2017 was a yearling colt in Gloucester County in late September. The colt was given an initial vaccination, but did not receive a booster shot. The colt is being treated. The other EEE viruses were reported in Atlantic and Cumberland counties.

EEE has a significantly higher risk of death in horses than West Nile Virus infection, with a 90 percent mortality rate for unvaccinated horses. Both viral diseases affect a horse’s neurological system and cause inflammation of the brain tissue. The diseases are transmitted by a mosquito bite. The viruses cycle between birds and mosquitoes with horses and humans being incidental hosts. EEE or WNV 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.

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.

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 –

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