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Protect Your Horses and Yourself from Mosquito-Borne Diseases EEE and WNV

By Laura Kenny
Eastern Equine Encephalitis has been reported in NJ and OH this summer. Learn about EEE and West Nile Virus and how to keep yourself and your horses safe.
With the announcements of several horses and humans contracting the rare and life-threatening disease Eastern Equine Encephalitis (EEE) in neighboring New Jersey and other states this summer, many are wondering if they or their animals are at risk.
The New Jersey Department of Health tests mosquito populations for the virus weekly, and as of September 7, record numbers of positive populations in 11 counties have been found. As of September 7, there were 9 equine cases and 1 human case of of EEE in 2019 in New Jersey. On the western border, there was a confirmed case of EEE in an Ohio horse in August.
While there have not been any horse or human cases of EEE in Pennsylvania this year, it has happened in the past. According to the PA DEP, in 2018 there was 1 human and 1 veterinary case of EEE in Luzerne County.
While less life-threatening, West Nile Virus (WNV) is far more prevalent in Pennsylvania. In 2018, there were 130 reported human cases and 112 equine cases. So far in 2019, there have been no human cases, but infected mosquitoes, birds, and animals (no horses) have been reported around the state. As of September 13, eight counties in southeast PA, Erie, and Westmoreland counties are considered “hot zones” with high risk of contracting WNV.
What do you need to know?
Both EEE and WNV are mosquito-borne diseases. They are both present in wild bird populations, and mosquitoes spread the virus. Horses (and humans) contract the virus when bitten by an infected mosquito and are considered “dead-end hosts”. The viruses cannot be transmitted from horse to horse, horse to human, or even horse to mosquito to human. Dead-end hosts are highly unlikely to have enough virus in their blood to infect a new mosquito.
There are vaccines for EEE and WNV available for horses (but not humans), and they are considered core vaccines. Pennsylvania horses require annual spring revaccination, and the American Association of Equine Practitioners recommends a booster if the horse is in an area where the disease is endemic or the horse is immunocompromised.
Keep yourself and your horses safe by using mosquito repellents and controlling mosquito populations around the barn and home. (Note: Pesticides, including repellents, are poisonous. Read and follow all label directions, restrictions, and safety precautions. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.)
Be aware that peak mosquito activity is from dusk to dawn, so you may want to avoid turnout during this period. Mosquitoes are attracted to light, so keep lights off in the barn overnight if horses are in. Fly sprays containing pyrethrin help to repel mosquitoes from horses. Keep chickens or other fowl separate from stables as they can become infected.
Dispose of all standing water you can find; mosquitoes can lay eggs in a vessel as small as a bottle cap. Don’t forget about tires, gutters, trash cans, and wheelbarrows. Troughs should be dumped and cleaned at least weekly, and mosquito dunks can be used safely in horse water.
If you suspect your horse may have EEE or WNV, contact your veterinarian immediately. They are both reportable diseases.