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Recently, mosquitoes infected with EEE (Eastern Equine Encephalomyelitis virus) were found in Voluntown, CT. Not only that, but there have been 2 confirmed cases of EEE positive horses in Massachusetts. While it would be nice to hide from it, the fact is that it is in our backyard. But what do we really know about it?
EEE is mainly found in the US east of the Mississippi river, and throughout areas of Central and South America. The virus persists in “reservoirs” – wild animals that carry the disease such as bats, rodents, and birds. A vector (such as a mosquito) becomes infected when it feeds on one of these animals. Most often, EEE is maintained through a transmission cycle between birds and mosquitoes. The mosquito then carries the virus for life and can transmit it through its saliva. If a horse happens to be the source of the next blood meal, then they can become infected and quickly begin to show signs.

Once infected, it takes approximately 5-15 days for signs to show up. These signs can be very mild such as a fever and depression; or severe including blindness, stumbling, seizures or death. Any neurologic signs could be indicative of EEE, however other diseases such as rabies must be considered as well, and a diagnosis should be confirmed via testing. Unfortunately, a diagnosis is often obtained post-mortem. If EEE is suspected, the state veterinarian must be contacted and the disease needs to be reported.

EEE is usually fatal in horses (75-100% mortality rate). They are considered dead-end hosts as there is typically not enough virus in the blood to infect another mosquito. This means that transmission from horses to humans, or even to another mosquito, is extremely unlikely. That being said, in acute infections, circulating virus can be high and outbreaks can occur in a horse-dense population.

The disease is seasonal and usually lasts from July to November in this area. It is mainly dependent upon the mosquito population, as they are the main vector. Warm temperatures and standing water promote mosquito reproduction.

Treatment for EEE consists of supportive care. There is not a cure for this disease. The best thing for EEE is prevention. Be sure that your horses are vaccinated. While vaccines are not always 100% effective they do lessen the severity of the disease. If your horse is vaccinated by a veterinarian, and your horse becomes infected, most drug companies carry a guarantee on that vaccine which will help with the finances of treatment. In this area, horses should be vaccinated yearly against this virus. We recommend the vaccine be administered sometime in the spring, prior to peak season.

It’s also important to control mosquito populations on your farm. This can be tricky, but simple steps can be taken including using fly sheets, or just removing old tires from your property. Old tires and items that collect standing water are breeding grounds for mosquitoes, so removing them greatly reduces your risk.

Eastern Equine Enecphalomyelitis is a scary disease, for humans and horses. Unfortunately it appears that it is becoming a more prominent disease in our area. Be sure to take measures to protect yourself as well as your horses, and always keep that fly swatter handy.