St. Louis Encephalitis

St. Louis Encephalitis is a disease caused by the mosquito borne St. Louis Encephalitis virus. St. Louis encephalitis virus is related to Japanese encephalitis virus. This disease mainly affects the United States. Occasional cases have been reported from Canada and Mexico.

Mosquitoes, from the genus Culex, become infected by feeding on birds infected with the St. Louis encephalitis virus. Infected mosquitoes then 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. Only infected mosquitoes can transmit St. Louis encephalitis virus. Once a human has been infected with the virus it is not transmissible from that individual to other humans.

The majority of infections result in mild illness, including fever and headache. When infection is more severe the person may experience headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions and spastic paralysis. Fatality ranges from 3-30%, aged people are more likely to have a fatal infection. In the United States an average of 128 cases of St. Louis encephalitis are recorded annually. In temperate areas of the United States, St. Louis encephalitis cases occur primarily in the late summer or early fall. In the southern United States where the climate is milder St. Louis encephalitis can occur year round.

There is no vaccine or any other treatments specifically for St. Louis encephalitis virus.