by Alison Bowler

Created on: September 17, 2011   Last Updated: September 18, 2011

Despite its name, the viral cause of Eastern Equine Encephalitis (EEEV) is primarily a pathogen of birds. The Field Manual of Wildlife Diseases states that the passerines and other perching birds, which harbor the virus, rarely show evidence of infection. The virus passes between its avian hosts via the bite of a mosquito, usually Culiseta melanura.  Other mosquito species may pass the virus to non-avian vertebrates such as humans and horses, which then may develop symptoms of clinical Eastern Equine Encephalitis.

The virus causing the infection is an RNA virus of the Alphavirus genus in the Togaviridae family. Viruses transmitted via the bite of an insect are also known as arboviruses, which comes from the terms arthropod and borne.

According to the Directors of Health Promotion and Education the virus occurs within certain geographical areas comprising of North America, Central and South America, and the Caribbean. Within the United States, most infections occur in the eastern seaboard states and the Gulf Coast and occasionally within some of the in land states with suitable habitat to support the mosquito vectors.

So what happens if a mosquito carrying EEEV bites a person? Well the majority of people will not exhibit any symptoms of infection some develop symptomatic disease. Two forms of symptomatic Eastern Equine Encephalitis are recognized and symptoms appear 4 to 10 days post the bite of an infected mosquito.

The first form is the systemic form this has an abrupt onset and symptoms include chills, fever, malaise, arthralgia, and myalgia. These symptoms persist  or 1 to 2 weeks and recovery is usually complete and uneventful.

The second form of Eastern Equine Encephalitis is the encephalitic form. In infants, this form presents with an abrupt onset. However, in older children and adults it normally follows a few days of symptoms characteristic of the systemic form of the illness. The symptoms of encephalitic Eastern Equine Encephalitis include fever, headache, irritability, restlessness, drowsiness, anorexia, vomiting, diarrhea, cyanosis, convulsions and coma. Unlike the systemic form encephalitic Eastern Equine Encephalitis the encephalitic form is potentially fatal and many of the survivors will suffer permanent brain damage. The Centers for Disease Control and Prevention estimate that in an average year of six cases of the encephalitic form of Eastern Equine Encephalitis occurs in the United States and the mortality rate of such infections is about 33%.

Treatment of eev relies on supportive therapy as at present none of the anti-viral therapies available has proved active against EEEV. As with all diseases prevention s better than cure, in the case of eev a vaccine is not available for human use although there is one for use in horses in endemic areas. Human EEEV infection prevention relies on avoiding mosquito bites by covering bare skin and the use of suitable insect repellants.

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