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. St. Louis encephalitis is the most common human disease caused by mosquitoes in the United States. Since 1964, there have been about 4,440 confirmed cases of St. Louis encephalitis, with an average of 130 cases per year.