St. Louis encephalitis is a rare mosquito-borne virus found only in the Americas. Most infections produce no symptoms at all, and symptomatic cases are uncommon. Severe encephalitis occurs primarily in elderly adults.
The virus is transmitted by Culex mosquitoes and circulates between birds and mosquitoes, with humans as incidental hosts. Small outbreaks occasionally occur in the United States during warm summer months, particularly in the Midwest and South.
There is no vaccine or specific treatment. The risk to travelers is extremely low, and standard evening bite precautions provide adequate protection.
Culex pipiens and Culex quinquefasciatus — night-biting house mosquitoes.
Adults over 60 traveling in the Americas during summer months. Most infections are so mild they go completely unnoticed. There is no vaccine or specific treatment.
St. Louis Encephalitis is recorded in 8 countries in our database. Click any country for the full Mozzwise briefing covering local seasonality, regional risk, and prevention.
Disease information is sourced from WHO, CDC, ECDC, and OpenDengue. Not medical advice. Personal decisions on diagnosis, treatment, vaccinations, or medication belong with a qualified healthcare professional.