Epidemiology, clinical features and prevention of HTLV‐I infection

Abstract

Human T-cell leukemia virus type I (HTLV-I) [1,2] is the main cause of Adult T-cell leukemia ⁄ lymphoma (ATLL) [3] and HTLV-I associated myelopathy ⁄ Tropical spastic paraparesis (HAM ⁄ TSP) [4,5]. From the long-term epidemiological observation, the HTLV-I carriers are clustered in limited groups in the world, i.e., Southwestern Japanese, native Oceanians, Amerindians in Andes and Northeast British Colombia, North Iranians as well as Central Africans and their descendants in the Caribbean basin and South America [6]. According to evidence obtained from a biennial nationwide surveillance of adult T-cell leukemia ⁄ lymphoma (ATLL) carried out in Japan since 1986, the annual incidence is estimated to be 700 within approximately one million HTLV-I carriers in Japan [7]. The affected individuals mainly inhabit the southern and northern ATLL endemic areas. Among 3499 ATLL patients newly diagnosed during the last ten years from 1988 to 1997 [8], approximately 70% were born in the southwestern districts of Kyushu and Shikoku, and 10% in the northern districts of Hokkaido and Tohoku (Fig. 1). This epidemic pattern of ATLL is still continuous up until now. The main reasons of unique geographical clustering of ATLL in Japan might be linked to a history of old Japanese migration with unique geographical clustering of HTLV-I carriers in Japanese archipelago due to the natural transmission routes of mother-to-child through breast milk and man-to-woman through semen [9,10]. In the ATLL endemic areas in Japan a systematic prevention trial against HTLV-I transmission through breast milk from HTLV-I carrying mothers to newborn babies, e.g., strong recommendation to pregnant women with HTLV-I to completely stop breast milk and ⁄ or to raise their babies by short-term breast feeding [11,12]. Clinically contrasting HTLV-I related diseases