Eastern Equine Encephalitis Virus

Eastern equine encephalitis virus (EEE), also called sleeping sickness or Triple E, is a zoonotic alphavirus and arbovirus that exists in the Americas and the Caribbean. It was first seen in Massachusetts in 1831 when 75 horses died of encephalitic illness. It is often associated with coastal plains.

EEE was first isolated from the brain of an infected horse in 1933. In 1938 the first human case was confirmed when thirty children died of encephalitis in northeaster United States coinciding with outbreaks in horses in the same regions. Fatality rate in humans is 35% with no current cure. Not only can it infect horses and humans, EEE can infect a wide range of mammals, birds, reptiles, and amphibians. A bird-mosquito cycle is responsible for the virus persisting in nature. There are two mosquito species responsible for the spread of the virus and they feed on the blood of birds which means during the summer when more birds and mosquitoes are feeding more of them are infected.

Mosquitoes that bring the virus from the avian population to a mammalian population are called bridge vectors. Generally people are only infected from a mosquito bite due to mammals not circulating enough of the virus in their blood to infect additional mosquitoes. Since the virus travels via lymphatics to the lymph nodes in often results in lymphopenia, leucopenia, and fever.

Symptoms in horses happen 1-3 weeks after infection and usually start with a fever. The fever usually lasts 24-48 hours and during this time sensitivity to sound, periods of excitement and restlessness occur. Brain lesions cause drowsiness, drooping ears, circling, aimless wandering, inability to swallow, and abnormal gait. Paralysis follows the lesions usually completely incapacitating the horse and leading to death 2-4 days after symptoms appear. Horse mortality rates range form 70% to 90%. The disease is preventable in horses through vaccinations, there is, however, no cure for EEE. Corticosteroids, anticonvulsants, and intravenous fluids are used as treatment.

Since 2004 several northeast US states have had an increase in virus activity. 10 human cases have been reported between 2004 and 2006. A Scottish citizen was the first European to be infected in 2007.