Detection of herpes simplex virus DNA in maternal breast milk by in situ hybridization with tyramide signal amplification.

In this study we investigated the prevalence of herpes simplex virus 1 (HSV-1) and 2 (HSV-2) in maternal breast milk using the technique of in situ hybridization combined with the sensitive detection system of tyramide signal amplification. Breast milk samples were collected from both breasts of 34 puerperals 4-5 days after delivery. HSV DNA was detected in 16 out of 34 examined breast milk specimens. HSV DNA was found in the milk of both breasts in 10 cases (62.5%), in that of left breast in 4 cases (25%) and in the milk of only the right breast in 2 cases (12.5%). HSV DNA was localized in the nuclei of mononuclear cells and to a lesser degree in the nuclei of epithelial cells. The number of HSV infected cells ranged from a few cells per sample to 20% of cells (mean value 9%, median value 5%). According to HSV typing, we found both HSV-1 and HSV-2 in 11 out of 16 positive cases and HSV-2 only in 5 cases. In conclusion, our findings indicate that HSV-1 and HSV-2 are shed into breast milk in a significant proportion of puerperals and breast-feeding may be an important route for the transmission of these viruses to infants.