St. Louis encephalitis is found throughout North, Central, and South America, and the Caribbean, but is a major public health problem mainly in the United States. The virus is found throughout the country, but periodic outbreaks and epidemics have occurred in the Mississippi Valley and Gulf Coast, the western states, and Florida. Humans and other mammals are not an important part of the life cycle of the virus. Sometimes, however, people who live in or visit an area where the virus lives can be infected by the bite of an infected mosquito. After infection, the virus invades the central nervous system, including the spinal cord and brain.
Symptoms are usually mild and include fever, headache, tiredness, and dizziness.
In its more severe form, the disease can cause convulsions and death. Diagnosis is based on tests of blood or spinal fluid. There is no specific treatment for St. Louis encephalitis. Antibiotics are not effective against viruses, and no effective anti-viral drugs have been discovered. Care of patients centers on treatment of symptoms and complications.