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Is West Nile virus now established in
the Western Hemisphere?
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?
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.