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New evidence for transmission of Zika virus via breast milk was reported in a brief report from Clinical Infectious Diseases.
Samples of breast milk, plasma, and urine were collected from a 32-year-old Venezuelan woman after she presented with a 1-day history of malaise, arthralgia, conjunctival hyperemia, and pruritic maculopapular rash. Samples of plasma and urine were also collected from her asymptomatic 5-month-old child, who at the time was exclusively breastfed.
Cytopathic effects characteristic of Zika virus infection were observed in Vero E6 and LLC-MK2 cells 9 and 12 days after inoculation with the mother’s breast milk and urine samples and the child’s plasma and urine samples.
Breast milk cultures were then screened for chikungunya virus; dengue viruses 1, 2, 3, and 4; and Zika virus genomic RNA by reverse-transcription polymerase chain reaction. All cultures were negative for chikungunya and dengue viruses and positive for Zika virus genomic RNA. The mother’s urine and child’s urine and plasma were also positive for Zika virus RNA.
Full genome sequencing of the Zika virus isolated from the breast milk and child’s urine revealed 99% similarity, and sequencing of the NS5 gene of the other isolates indicated that mother and child were infected with the identical virus.
The strains of virus isolated from the patients clustered with high-bootstrap support (99%) within a larger clade of strains isolated from Colombia, according to phylogenetic analysis. The mother and child had no recent travel history and lived in an air-conditioned, screened house in Venezuela where mosquito transmission would be limited. While the precise source of the child’s infection cannot be determined, these results strongly suggest postnatal transmission via breast milk.
Reference
Blohm GM, Lednicky JA, Márquez M, et al. Evidence for mother-to-child transmission of Zika virus through breast milk [published online December 30, 2017]. Clin Infect Dis. doi: 10.1093/cid/cix968
