ST. LOUIS ENCEPHALITIS
St. Louis encephalitis is a mosquito-borne viral disease with the potential of infecting the central nervous system of people. It is the most commonly reported variety of viral encephalitis in the United States, but is not nearly as common in Canada.
St. Louis encephalitis virus (SLEV) is an arbovirus (arthropod-borne virus) that causes St. Louis encephalitis (SLE). It is closely related to the West Nile virus. Other important encephalitis arboviruses include the eastern equine encephalitis virus, western equine encephalitis virus, and La Crosse encephalitis virus. SLEV was named for St. Louis, Missouri, where the first and largest epidemic occurred in 1933.
The natural hosts of SLEV are birds such as finches, sparrows, blue jays, cardinals, mockingbirds, blackbirds, robins, and doves.
SLEV is passed from one bird to another by the bite of a mosquito. When a mosquito bites an infected bird, the virus replicates in the mosquito and moves to other locations in the mosquito’s body, including the salivary glands. When the mosquito takes its next meal from an uninfected bird, it deposits a small drop of saliva where it bites to act as an anticoagulant. The saliva contains the virus, which enters the bird, replicates, and becomes a source of virus for other mosquitoes. Birds are considered amplifiers of SLEV, because one bird can potentially infect many mosquitoes (Figure 34).