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Is West Nile virus now established in the Western Hemisphere?
A. The continued expansion of West Nile virus in the United States indicates that it is permanently established in the Western Hemisphere.
Is the disease seasonal in its occurrence?
A. In the temperate zone of the world (i.e., between latitudes 23.5° and 66.5° north and south), West Nile encephalitis cases occur primarily in the late summer or early fall. In the southern climates where temperatures are milder, West Nile virus can be transmitted year round.