The effects of breastfeeding and presence of antibody to p40tax protein of human T cell lymphotropic virus type-I on mother to child transmission.

We examined the effects of various factors, including duration of breastfeeding, the status of mother's anti-p40tax, and titre of mother's anti-human T cell lymphototropic virus type-I (HTLV-I) on mother to child transmission of HTLV-I in 76 HTLV-I carrier mothers and 175 of their children. The overall prevalence of anti-HTLV-I among children was 16.0%. The prevalence of anti-HTLV-I among children breastfed for over 3 months was significantly higher (27.6%) than that of those breastfed for under 3 months (5.1%; P = 0.012). Of the 78 bottle-fed children, 10 (12.8%) were positive for anti-HTLV-I. In the children breastfed for over 3 months, the prevalence of anti-HTLV-I among 37 children of anti-p40tax positive mothers was 37.8% and that of 21 children of anti-p40tax negative mothers was 9.5%, a significant difference (P = 0.044). These data suggest that about 13% of bottle-fed children born to carrier mothers are infected with HTLV-I by routes other than breast milk, and that the mother's anti-p40tax can serve as a marker of infectivity of HTLV-I in the case of breastfeeding for over 3 months.