Although human T-cell lymphotropic viruses (HTLV-1/2) were described over 30 years ago, they are relatively unknown to the public and even to healthcare personnel. Although HTLV-1 is associated with severe illnesses, these occur in only approximately 10% of infected individuals, which may explain the lack of public knowledge about them. However, cohort studies are showing that a myriad of other disease manifestations may trouble infected individuals and cause higher expenditures with healthcare. Testing donated blood for HTLV-1/2 started soon after reliable tests were developed, but unfortunately testing is not available for women during prenatal care. Vertical transmission can occur before or after birth of the child. Before birth, it occurs transplacentally or by transfer of virus during cesarean delivery, but these routes of infection are rare. After childbirth, viral transmission occurs during breastfeeding and increases with longer breastfeeding and high maternal proviral load. Unlike the human immunodeficiency virus types 1 and 2, HTLV is transmitted primarily through breastfeeding and not transplacentally or during delivery. In this study, we review what is currently known about HTLV maternal transmission, its prevention, and the gaps still present in the understanding of this process.

Objective: Although HTLV-1 is associated with severe diseases, there is ongoing vertical transmission since prenatal HTLV screening is not implemented in countries where the virus is present. We performed a cross-sectional analysis to verify the impact of counseling pregnant HTLV-1 seropositive women, who participate in the GIPH cohort study in Brazil, on this vertical transmission.Methods: GIPH study started in 1997 as an open prevalent cohort of HTLV-positive individuals. Children born from HTLV-1 seropositive women were divided into: (1) born before and (2) after the participation of mothers in the GIPH cohort ("GIPH babies"). The pregnant women participating in the study were counseled in order to prevent viral transmission, with recommendations of avoiding breastfeeding, giving infant formula, and preferably having the delivery by cesarean section. Results:We identified 54 children born of HTLV seropositive mothers. 3/21 (14.3%) of the children born from mothers who received no counseling were found positive for HTLV-1, in contrast to 1/18 (5.6%) of the "GIPH babies", whose mothers received counseling. 15 children were not tested, either due to the family's refusal or impossibility to locate them. Discussion:We found that it was worthwhile to counsel the mothers, since, as previously reported in the literature, we could observe a decline in the vertical transmission, which demonstrates the importance of prenatal screening of the virus. These actions should be widespread in countries where HTLV is present, in order to avoid the silent transmission of HTLV and future diseases in children born from positive mothers.