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. Up to 3,000 cases have been reported during epidemics in some years.
Many more infections occur without symptoms and go undiagnosed.
The virus was first isolated in 1933 during an epidemic in St. Louis, Missouri, and has re-emerged often in epidemics in the United States. The largest outbreaks in 15 years occurred in 1990 in Florida and Texas. The risk of exposure is increasing in urban areas as deteriorating inner cities create new habitats for mosquitoes. There is no vaccine to prevent St. Louis encephalitis. Prevention centers on public health action to control mosquitoes and on individual action to avoid mosquito bites.