[Studies on factor affecting mother-to-child HTLV-I transmission]

Epidemiological data indicate that breast feeding is the primary route of mother-to-child transmission of HTLV-I. However, serological studies show that 60 to 90% of infants who are fed breast milk from HTLV-I carriers avoid HTLV-I infection. To understand the mechanism of the virus transmission, the titer of HTLV-I antibodies and p40tax antibody and the copy number of the HTLV-I proviral DNA in peripheral lymphocytes in the HTLV-I carrier-mothers were surveyed. The seroprevalence of HTLV-I in the children born to carrier mothers was 6.1% in a normal breast feeding group, 7.7% in a group fed with freeze-thawed breast milk and none in a bottle-fed group. The difference between the seroconversion rate for the normal breast feeding group and others was statistically insignificant. Our studies also indicated that neither the titer of HTLV-I antibodies in carriers nor the duration of breast feeding was relevant to seroconversion in the children. The seroconversion rate in children was higher in p40tax antibody-positive mothers than in a seronegative group, but the difference was statistically insignificant. In conclusion, the copy number of the HTLV-I provirus in the lymphocytes of the carrier mothers was the most relevant factor in the seroconversion of infants who received breast milk from HTLV-I carriers.