Transmission routes of HTLV-I: an analysis of 66 families.

HTLV-I transmission routes were found for 66 carrier pregnant women by studying sera, from the carrier pregnant women, their mothers, and their husbands, and by obtaining detailed family histories at interview. Forty-one cases (62.1%) were considered to be instances of vertical transmission, 15 (22.8%) of sexual transmission, 6 (9.1%) of blood transfusion, and 4 (6.1%) undecided. To date, most cases of adult T-cell leukemia (ATL) have been considered to result from vertical transmission. Our results therefore imply that about 30% (22.8% + 9.1%) of the carrier pregnant women are at minimal risk of ATL. Moreover, in case of presumed husband-to-wife transmission, more than half (6/11) were infected between one year and four years after marriage.