West Nile Virus Encephalitis in America

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Abstract
Molecular diagnostic techniques, including the amplification of viral nucleic acid from cerebrospinal fluid by the polymerase chain reaction (PCR), have revolutionized the diagnosis of viral infections of the central nervous system.1 Nevertheless, the causes of about two thirds of cases of presumed viral encephalitis remain unknown. In the United States, most cases of acute encephalitis are caused by herpes simplex virus (HSV), enteroviruses, and arthropod-borne viruses (arboviruses). Only arboviruses produce epidemics of viral encephalitis. Arboviruses represent a functional rather than a taxonomic group, linked by the importance of mosquito and tick vectors in their transmission, and their epidemiologic features, including seasonal incidence and geographic distribution, are constrained by the ecology of their transmitting vectors. The arboviruses that cause encephalitis in the United States include the St. Louis, California, western equine, and eastern equine encephalitis viruses.