Mosquito-Borne Diseases EEE and WNV
Late summer and fall are prime seasons for the spread of both Eastern Equine Encephalitis (EEE) and West Nile Virus (WNV). For more information on the diseases and symptoms in humans, read the CDC websites on EEE and WNV. For more information on the diseases and symptoms in horses, read the Equine Disease Communications Center/American Association of Equine Practitioners fact sheets on EEE and WNV.
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. Both diseases are reportable.
For more information, refer to the following sources:
