Key points
- St. Louis encephalitis is caused by a virus primarily spread to people through the bites of infected mosquitoes.
- St. Louis encephalitis virus is maintained in the environment between mosquitoes and birds.
- People do not spread the infection other than rarely through blood transfusions.
Primary cause
St. Louis encephalitis is caused by a virus that is found in North and South America.
The virus belongs to a group of viruses called flaviviruses. Other medically important flaviviruses found in the United States include West Nile virus and Powassan virus.
How it spreads
- St. Louis encephalitis virus circulates in the environment between mosquitoes (primarily Culex species) and birds.
- People become infected with the virus when mosquitoes feed on infected birds and then bite people.
- People are considered dead-end hosts because unlike birds, they do not develop high enough levels of virus in their bloodstream and cannot pass the virus on to other biting mosquitoes.
- The virus is not transmitted from person-to-person, except rarely by blood transfusion.
- Because the virus can be transmitted through blood, persons who were recently diagnosed with St. Louis encephalitis virus infection should not donate blood and bone marrow for 120 days following infection.
- Prevent getting sick with St. Louis encephalitis by preventing mosquito bites.
Keep Reading:
Transmission of St. Louis Encephalitis Virus