Epidemiological features of HTLV-I and adult T cell leukemia.

Adult T-cell leukemia (ATL) patients and human T-cell leukemia virus type I (HTLV-I) carriers are clustered in limited groups in the world, especially among Japanese in Asia, Blacks in Central Africa, Melanesians in Papua New Guinea and Andeans in South America. The major transmission routes of HTLV-I under natural conditions are from mother-to-child through breast milk and from man-to-woman through semen. The whole life risk of ATL among persistent HTLV-I carriers is estimated at 2-6%. The detailed manifestation mechanism of ATL is not yet clarified; however, it is certain that HTLV-I infection in infancy is the main cause of ATL. Therefore, the prevention measure against mother-to-child transmission of HTLV-I is indispensable from a viewpoint of public health.