Milk-borne transmission of HTLV-I as a major route in the endemic cycle.

Mother-to-child transmission of HTLV-I as a major route in the endemic cycle of HTLV-I was established by epidemiologic evidence that (1) 22% (17/78) of children of HTLV-I carrier mothers were themselves carriers, in contrast to approximately 1% of the young age population of the same area, (2) more than 95% (23/24) of mothers of carrier children were themselves carriers, and (3) the product of the prevalence of carrier mothers and the incidence of carriers in children born to them corresponded well to the prevalence of carrier children in the same area. Intrauterine infection was not likely, since none of over 200 cord bloods of babies born to carrier mothers showed infection markers, such as IgM antibody or viral antigens. The possibility of milk-borne transmission was supported by (1) the presence of sufficient numbers of infected T-cells in the milk of carrier mothers, (2) the fact that a common marmoset was found to be a carrier after oral administration of the milk of carrier mothers, and (3) a retrospective analysis which revealed that none of nine babies fed only compound milk were carriers. An ongoing intervention study showed that none of 47 babies whose mothers refrained from breast feeding had seroconverted at 12 months of age. Compound milk feeding by carrier mothers seems to be an effective measure to reduce dramatically the infection rate of HTLV-I.