Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia-lymphoma (ATL), which is difficult to cure. In Japan, more than 1000 cases of ATL are diagnosed annually and the lifetime risk of ATL in HTLV-1-infected individuals is approximately 5%. 1 When acute transformation of ATL occurs, chemotherapy is the first choice of curative therapy. Median survival time in Japan, however, ranges from 7.4 to 13.0 months, despite various chemotherapy protocols to cure aggressive ATL. 2 Therefore, we have to acknowledge that ATL still has a poor prognosis. HTLV-1 is transmitted vertically from mother to child by breast-feeding, and horizontally by blood transfusion or sexual transmission. 3 ATL develops after a long incubation period (median age of onset, 67 years), mainly after mother-to-child transmission. 1 It is not possible to prevent the development of ATL or other HTLV-1-associated disorders in carriers of the virus. Therefore, primary prevention of mother-to-child transmission is the only strategy likely to reduce HTLV-1 carrier status and HTLV-1-related disorders in the next generation. 3 Japan is a highly endemic area for HTLV-1, with a particularly high prevalence in Kyushu Island. In Nagasaki, Kyushu, HTLV-1 screening of pregnant women has been in operation since 1987. 4 Among the total carriers in Japan, the percentage of HTLV-1 carriers in Kyushu decreased significantly from 50.9% in 1990 to 45.7% in 2007, while that in the greater Tokyo area increased from 10.8% to 17.7%. 5 The observed changes were considered to be mainly due to population migration from Kyushu to the metropolitan areas. 5 It was found that HTLV-1 carriers spread throughout the country. Therefore, to