Intervention of maternal transmission of HTLV-1 in Nagasaki, Japan.

Seroepidemiological and laboratory virological evidences strongly suggested that endemicity of HTLV-1 in Nagasaki Japan depends on maternal infant infections via breast milk. The most obvious way to prove this concept was an intervention study with refraining from breast-feeding by carrier mothers. Most infected babies seroconverted by the age of 12 months, which made it possible to diagnose the infection at the age of 12 months for the statistical purpose. Serology and PCR on both adults and children were consistent each other, suggesting the absence of seronegative carriers. The intervention study revealed that approximately 80% of maternal infection was prevented by refraining from breast feeding by carrier mothers. The remaining fraction of infections in formula-fed babies suggested an alternative infection pathway. Although intrauterine infections has been suggested by others to explain the PCR-positive cord blood samples. However, groups of cord blood-positive children and seroconverted children were distinct each other. Therefore, the presence of HTLV-1 provirus in the cord blood can not be a marker of intrauterine infection. Mothers who infected a child has approximately 10 times higher risk of another infection for the next baby than those who did not.