Zika virus transmission via breast milk in suckling mice

Objectives Infectious Zika viral particles were detected in human milk; however, whether they can be transmitted via breastfeeding remains unknown, so our objective was to clarify this. Methods Here, in a natural breastfeeding model, wild-type (C57Bl/6; WT) or interferon α/β (IFNα/β) receptor-deficient (A129; KO) murine dams on day 1 post-delivery were infected with Zika virus (ZIKV) intraperitoneally, and the neonates were suckled. In a novel artificial feeding model, WT suckling mice at 1 day old were fed with ZIKV alone or ZIKV and human breast milk mixtures. Thereafter, the virus distribution, clinical progression and neuropathology in the WT or KO neonates were characterized to evaluate the risk of ZIKV transmission through breast milk. Results In natural breastfeeding, viral RNAs (8/8) and infectious viral particles (7/8) were extensively present in the mammary glands of KO dams. All tested KO neonates (5/5), and none of WT neonates (0/9), were infected with ZIKV. In artificial feeding, 100% of the WT neonates (two groups, 12/12 and 16/16) were infected and developed some signs of neurodegeneration. ZIKV tended to seed and accumulate in the lungs and were subsequently disseminated to other tissues in both 16 naturally suckled and 19 artificially fed infected neonates. As human breast milk was mixed with ZIKV and fed to WT neonates, 45% individuals (9/20) were infected; in the infected neonates, the viral spread to the brain was delayed, and the clinical outcomes were alleviated. Conclusions These results demonstrated that suckling mice can be infected with ZIKV through suckling, and breast milk has potential antiviral activity, inhibiting ZIKV infection.