OBJECTIVES:

Infectious Zika viral particles were detected in human milk; however, whether they can be transmitted via breastfeeding remains unknown.

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 breastfed. In a novel artificial feeding model, WT suckling mice born at 1 day 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 highly presented in the mammary glands of KO dams, respectively. All tested KO neonates (5/5), while none of WT neonates (0/9) were infected with ZIKV. In artificial feeding, 100% 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 subsequently disseminated to other tissues in both 16 natural breastfeeding and 19 artificial feeding 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 could be infected with ZIKV through breastfeeding, and breast milk had potential antiviral activity inhibiting ZIKV infection