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St. Louis Encephalitis

St. Louis encephalitis is a viral infection of the central nervous system transmitted by the bites of infected mosquitoes. Infected mosquitoes transmit the St. Louis encephalitis virus to humans and animals during the feeding process. The St. Louis encephalitis virus grows both in the infected mosquito and the infected bird, but does not make either one sick.

Occurrence: St. Louis encephalitis outbreaks can occur throughout most of the United States. In temperate areas of the United States, St. Louis encephalitis cases occur primarily in the late summer or early autumn/fall. In the southern United States where the climate is milder St. Louis encephalitis can occur all year round. The last major epidemic of St. Louis encephalitis occurred in the Midwest from 1974-1977.

Manifestations: After an incubation period for usually 5 to 15 days illness begins. In the case of mild infections these occur without apparent symptoms other than a fever & headache. More severe infections are marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors & occasional convulsions (especially in infants) Spastic (but rarely flaccid) paralysis. Illness is fatal in 8% of cases overall and 20% of cases in persons over 60 years of age.

Diagnosis and treatment: Diagnosis is based on taking a blood test or testing the cerebro-spinal fluid. There is no specific treatment. Intensive support treatment is seen as the only treatment.

Vaccine: Not available

Prevent St Louis encephalitis by:
• Avoid mosquito bites by remaining in well screened areas
• Avoid mosquito bites by remaining in air-conditioned areas.
• Use mosquito repellents on skin and clothing
• Bring aerosol insecticides to use indoors
• Use bed nets.