If the mother has developed a primary infection with Herpes, she was
viremic before she developed the rash.  The baby will already have
picked up the virus through the milk, if the baby indeed picked it up,
which is not necessarily the case.  The problem with herpes infection is
systemic infection and/or encephalitis which may be fatal or may leave a
child neurologically damaged.  Once the baby is over about 4 weeks of
age, however, the risk of systemic and/or central nervous system
infection decreases to adult levels (which are not zero, but low).
Furthermore, the risk of systemic infection and/or encephalitis with
Herpes is mostly from Herpesvirus 1.  The genital infection is usually
Herpesvirus 2.

        If the infection is secondary, the mother's milk will contain
antibodies to herpesvirus, though this is not necessarily protection.

        After all is said and done, there is no reason to discontinue
breastfeeding.  To repeat, the mother's taking acyclovir is not a
contraindication to breastfeeding.

Jack Newman, MD, FRCPC