You may have heard or read in the news about Eastern Equine Encephalitis (EEE) causing human deaths recently. EEE is a rare virus transmitted to people and horses by the bite of an infected mosquito. Eastern Equine Encephalitis has been detected recently in 22 mosquito samples and in three horses in the southern and eastern parts of the U.S.

There is also a Western strain (WEE) and the two are closely related diseases that affect the horse's nervous system. They are both caused by an alphavirus, but EEE usually occurs in the South and East while WWW occurs in the West.

Typically, horses are vaccinated annually against EEE/WEE in the spring, at the start of mosquito season. However, there are many areas where mosquitoes remain active year round. For those areas, a booster vaccine in the fall may be recommended. The vaccine contains inactive versions of both viruses that stimulate the immune system to create antibodies.

Horses do not infect each other directly, but rather a mosquito bites an infected horse, then bites a uninfected horse or human and spreads the disease. That’s why it’s important for horse owners to take precautions against mosquito bites as well. You can do this by using insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus on exposed skin and/or clothing.

It’s always a good idea to talk with your equine veterinarian about what fall shots he recommends for your horse. These may include vaccines against rabies, tetanus and flu/rhino.