JE virus is the most common vaccine-preventable cause of encephalitis in Asia, occurring throughout most of Asia and parts of the western Pacific (Map 3-08). Local transmission of JE virus has not been detected in Africa, Europe, or the Americas. Transmission principally occurs in rural agricultural areas, often associated with rice cultivation and flood irrigation. In some areas of Asia, these ecologic conditions may occur near, or occasionally within, urban centers. In temperate areas of Asia, transmission is seasonal, and human disease usually peaks in summer and fall. In the subtropics and tropics, seasonal transmission varies with monsoon rains and irrigation practices and may be prolonged or even occur year-round.