St. Louis encephalitis virus (SLEV) is a spherical, single-stranded RNA virus with a diameter of 40 nm. It is a member of the Flaviviridae family. The vectors are mosquitoes in the Culex species: Cx. tarsalis and members of the Cx. pipiens complex in the western United States, Cx. pipiens and Cx. quinquefasciatus in the east, and Cx. nigripalpus in Florida.
Birds are the reservoir hosts of SLEV. Birds are not ill with the virus but infect the mosquitoes that bite them. In urban and suburban areas, blue jays, robins, house sparrows, and pigeons are the main birds involved. People and other domestic animals can be infected but do not develop viremia; therefore, they are "dead-end" hosts.
Figure 33. Transmission of St. Louis encephalitis virus. (2024). Centers for Disease Control and Prevention. https://www.cdc.gov/sle/php/transmission/index.html
Figure 34. Public health domain. (1975). Image #10228. This transmission electron microscopic (TEM) image revealed the presence of numerous St. Louis encephalitis (SLE) virions that were contained within a mosquito salivary gland tissue sample. Centers for Disease Control and Prevention. https://phil.cdc.gov/Details.aspx?pid=10228
