Flavivirus Encephalitis

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Abstract
During the summers of 2002 and 2003, North America was affected by its largest-ever outbreaks of arboviral encephalitis. West Nile virus caused 2942 cases of meningitis or encephalitis in 2002, with 276 deaths, and 2866 cases in 2003, with 246 deaths.1,2 West Nile virus, which in the United States was first detected in New York in 1999, is one of several mosquito-borne neurotropic members of the Japanese encephalitis (JE) serogroup of the genus flavivirus, family Flaviviridae, that cause similar disease patterns across the globe ( Figure 1 and Table 1 ). These include St. Louis encephalitis virus in the United States, Rocio virus, which has caused encephalitis outbreaks in Brazil, and Murray Valley encephalitis virus in Australia, New Guinea, and New Zealand. Kunjin virus, which also circulates in Australia, recently has been reclassified as a subtype of West Nile virus. In terms of numbers, the most important member of the group is Japanese encephalitis virus, which causes an estimated 30,000 to 50,000 cases of encephalitis and 10,000 deaths in Asia every year.3 In addition to viruses of the JE serogroup, the flavivirus genus includes mosquito-borne causes of hemorrhagic fever (e.g., yellow fever and dengue viruses, which also occasionally cause encephalitis) and tick-borne viruses,4 which are not discussed here.