Zika virus shedding in human milk during lactation: an unlikely source of infection?

Zika virus (ZIKV) transmission through non-mosquito-dependent routes has become increasingly important since reports of sexual transmission. Breastfeeding is a potential means of ZIKV transmission, but data on this remain limited. The cases of four mothers with laboratory-proven infections are reported. No disease evolved in three of the breastfed babies despite detectable maternal viremia and viruria, the presence of viral RNA shedding, and the isolation of infective particles in one milk sample. Fever and rash in one infant of a ZIKV-infected mother proved to be related to chikungunya virus infection. The results suggest that the presence of infective particles in breast milk may not be sufficient for the efficient perinatal transmission of ZIKV.