MALE-TO-FEMALE TRANSMISSION OF HUMAN T-CELL LYMPHOTROPIC VIRUS TYPE-IAND TYPE-II - ASSOCIATION WITH VIRAL LOAD

Risk factors for male-to-female sexual transmission of human T-lymphot ropic virus types I and II (HTLV-I/II) were investigated among HTLV-se ropositive volunteer blood donors and their long-term (greater than or equal to 6 month) sex partners. Direction of transmission in concorda ntly seropositive pairs was assessed by analyzing risk factors for HTL V infection. Donors and their partners were also questioned regarding sexual behaviors during their relationships; HTLV antibody titers and viral load were determined for specimens from male partners. Among 31 couples in whom HTLV-infected men likely transmitted infection to thei r partners (11 HTLV-I and 20 HTLV-II) and 25 male-positive, female-neg ative couples (8 HTLV-I and 17 HTLV-II), HTLV transmitter men had been in their relationships longer (mean 225 months vs. 122 months) and ha d higher viral loads (geometric mean 257,549 vs. 2,945 copies/300,000 cells for HTLV-I; 5,541 vs. 118 copies/300,000 cells for HTLV-II) than non-transmitters (P = 0.018 and P = 0.001 for duration of relationshi p and viral load, respectively, logistic regression analysis). Transmi tter men also tended to have higher antibody titers against various en v and whole virus proteins than non-transmitters. The identification o f high viral load and duration of relationship as risk factors provide s a biologically plausible framework in which to assess risk of sexual transmission of the HTLVs.