What is St. Louis Encephalitis?

St. Louis encephalitis one of the most common mosquito-borne illnesses in the Americas. The virus responsible for St. Louis encephalitis belongs to the Flavivirus genus. It is passed from infected birds to mosquitoes, who feed on the birds, and then to humans; it is not passed human to human. Most cases are in the U.S., but the virus is also encountered in Central America, South America, and the Caribbean. Once someone displays symptoms, the only treatment is to make the infected person as comfortable as possible until the illness runs its course.

The virus was discovered in 1933. Between the years 1955 and 1988, 5000 cases of St Louis encephalitis were reported to the U.S. Centers for Disease Control. In 1990, Florida and Texas sustained one of the largest epidemics in more than 15 years. Impoverished areas of the Gulf coast and western states tend to be the areas where most outbreaks of the illness occur. Most cases emerge in the late summer or early fall.

This arbovirus, or virus passed by arthropods, is closely related to the Japanese encephalitis virus, the Dengue virus, and the yellow fever virus. When the Culex mosquito species feeds on an infected bird, the mosquito contracts the virus. Doves, sparrows, finch, blue jays, and robins are often carriers. The infected mosquito then bites a human and passes the virus along to him or her.

Once infected with St. Louis encephalitis, the brain, spinal cord and the rest of the central nervous system are invaded by the virus where it incubates for 5-21 days. People may or may not show symptoms; if they do have symptoms, headache, fever, dizziness, and fatigue are the most likely. More severe symptoms include stupor, coma, spastic paralysis, neck stiffness, tremors, and seizures, with the illness being fatal in 3 to 30% of cases. Acute symptoms can last up to one week, but it may take weeks or months to feel completely healthy again.

A positive diagnosis is made with a blood test. There are no anti-viral drugs or vaccines to prevent St Louis encephalitis. Everyone is at risk. The elderly, those who spend a lot of time outside, and people living in impoverished areas are most at risk. The best way to prevent the virus is to avoid mosquito bites.

Among various precautions, doctors recommend staying inside between dusk and dark when mosquitoes are most active. Doctors also suggest wearing long pants and long-sleeved shirts outside, and using insect repellent with DEET, picaridin, IR3535, or oil of lemon eucalyptus. Mosquito breeding grounds, i.e., anywhere with standing water, should be emptied, if possible.