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Neonatal Herpes (primary infection of the newborn)

Neonatal herpes is the term used when a baby develops symptoms of herpes infection before he/she is born or within the first 6 weeks of life. It may occur when the baby is still in the womb (intra uterine/congenital infection) (<5%), during delivery (85%), or after delivery (less than 15%). The estimated rate of neonatal herpes is one case in 2,000-5,000 deliveries a year, resulting in approximately 1,500 to 2,200 infants with the disease each year in the United States.

Forty percent of neonatal herpes is confined to the skin, eye and mouth (SEM). The brain is involved (encephalitis) in 35 % of cases, with or without skin lesions. The poorest outcome is for the 25% of neonates who present with widespread (disseminated) disease, involving the lungs, liver, adrenal glands, skin, eye and mouth. Sixty percent to 75% of these infants also have encephalitis and more than 20% do not have skin lesions.

Intrauterine HSV infection can result from either primary or recurrent maternal infection, causing congenital herpes. Congenital herpes may not be obvious at birth, but may reveal itself later by the occurrence of skin lesions.

The highest risk (50%) for the baby is if the mother has a true primary infection at the time of delivery. Measuring type specific HSV IgM antibody in maternal blood may help to define the infection type. However, such measurements are not fool proof, as HSV IgM antibodies may also indicate recurrent disease. Culture or antigen analysis of genital lesions will tell us the type of virus present (HSV-1 or HSV-2) but cannot distinguish a primary disease from a recurrent one.

For infants born to mothers who have a new infection (primary or initial) near to the time of delivery, the risk for neonatal herpes is around 30%. The risk for transmission in infants born to mothers with known genital herpes and is very low (less than 1%).. This variation in risk can be partly explained by the fact that maternal HSV IgG antibodies are transported across the placenta to protect the fetus. These antibodies are present if the mother has been infected with HSV before the middle of pregnancy. Furthermore, the presence of maternal antibodies specific to HSV-2, but not HSV-1, appears to reduce the transmission of HSV-2 to the neonate.

At least 4 factors increase the risk of transmission of infection from an HSV seropositive mother to the fetus or neonate:

  • the mother has primary or initial infection during pregnancy
  • the mother has no HSV antibodies at delivery
  • prolonged rupture of membranes (>6 hours) (ascending infection)
  • the use of fetal scalp monitors.