Milk-borne transmission of HTLV-I from carrier mothers to their children.

In order to clarify the natural transmission route of human T-cell leukemia virus type I (HTLV-I) from mother to child, we have followed two groups of children with ages of 1 to 3 years who were nourished either with HTLV-I-infected breast milk, or with non-infected milk from sero-positive, HTLV-I carrier mothers. Tests for the presence of antibody against HTLV-I revealed that 4 of 6 children in the former group developed HTLV-I infection, while only 1 of 14 children in the latter group became infected. The difference in HTLV-I infection rate for the children in the two groups was statistically significant (P less than 0.01 by chi-square). Furthermore, 2 of 4 elder siblings in the former group developed HTLV-I infection, whereas only one of 8 elder siblings in the latter group became infected. The overall rate of HTLV-I infection of breast-fed children born to HTLV-I-carrier mothers was 25% (8/32) by 3 years of age. Five of 6 mothers with HTLV-I-infected cells in the milk also possessed infected cells in their peripheral blood. Conversely 5 of 6 mothers without infected cells in the peripheral blood possessed no infected cells in their breast milk, suggesting that HTLV-I-infected cells in the peripheral blood can enter the breast milk. None of the 8 breast-fed children born to carrier mothers whose peripheral blood and breast milk-borne cells were negative, developed HTLV-I infection, suggesting that HTLV-I transmission from mother to child is dependent upon the number of HTLV-I-infected cells in carrier mothers.