Herpes simplex virus (HSV), including types 1 and 2, is a common infection causing painful sores on the mouth or genitals. While usually manageable for adults, transmission to a developing fetus or newborn is a serious concern for expectant parents. Understanding how the virus can be passed from mother to baby is important for assessing risk. Although the overall incidence is low, neonatal herpes can lead to severe long-term disability or death if not treated promptly.
Understanding Congenital Herpes
A baby can contract herpes while still in the womb, known as congenital herpes. This occurs when the virus crosses the placenta and directly infects the fetus. This form of transmission is exceedingly rare, accounting for less than 5% of all neonatal herpes cases. The highest risk for congenital infection occurs when a mother experiences a primary HSV infection during the first or second trimester of pregnancy.
During a primary infection, the mother has not yet developed protective antibodies, allowing the virus to travel through the bloodstream and potentially reach the placenta. Transmission early in gestation can lead to severe outcomes such as miscarriage, stillbirth, or significant congenital anomalies. These anomalies may include chorioretinitis, microcephaly, and skin scarring. The risk of congenital transmission from a recurrent maternal outbreak is much smaller because the mother’s existing antibodies offer protection to the fetus.
The Primary Risk: Transmission During Delivery
The most frequent way a baby acquires herpes is during childbirth, known as intrapartum transmission, accounting for approximately 85% of cases. This happens when the infant passes through the birth canal and contacts the virus shed from active genital lesions or asymptomatic viral shedding. The risk of transmission is significantly higher if the mother experiences a primary genital herpes outbreak late in the third trimester.
In this scenario, the mother’s immune system has not had sufficient time to produce and pass protective antibodies to the baby, resulting in a transmission risk as high as 30% to 50%. In contrast, a mother with a history of recurrent genital herpes has a much lower risk, typically 2% or less, because her antibodies are shared with the fetus. A cesarean delivery reduces the infant’s exposure to the virus in the birth canal. This procedure is strongly recommended when a mother has active genital lesions or prodromal symptoms at the time of labor, though it does not eliminate the risk entirely.
Identifying Symptoms in Newborns
Neonatal herpes symptoms can manifest anytime from birth up to six weeks of age, but they typically appear within the first four weeks. The clinical presentation is divided into three categories based on the extent of the infection. The first, and least severe, is skin, eyes, and mouth (SEM) disease. This is characterized by fluid-filled blisters that may cluster on the skin, though some infants may only have an infection of the eyes or mouth.
The second form is central nervous system (CNS) disease, where the virus affects the brain and spinal cord, potentially causing encephalitis. Infants with CNS involvement may exhibit subtle symptoms such as fever, poor feeding, lethargy, or seizures, and they may or may not have skin lesions. The third and most severe form is disseminated disease, where the virus has spread to multiple internal organs, including the liver, lungs, and adrenal glands. Disseminated infection can resemble bacterial sepsis, presenting with symptoms like breathing difficulties, jaundice, and shock. This form carries the highest risk of mortality.
Protecting the Baby: Prevention and Treatment
Preventative strategies focus on reducing the baby’s exposure to the virus, especially during the peripartum period. For mothers with a history of recurrent genital herpes, suppressive antiviral therapy (typically acyclovir or valacyclovir) is offered starting at 36 weeks of gestation. This daily medication decreases the frequency of recurrent outbreaks and reduces asymptomatic viral shedding at delivery.
If an active lesion or prodromal symptoms are present at the onset of labor, a cesarean section is performed to bypass the infected birth canal. For newborns suspected or confirmed to have neonatal herpes, immediate treatment with intravenous antiviral medication, such as high-dose acyclovir, is initiated. The duration of intravenous therapy varies, often lasting 14 to 21 days or longer for CNS or disseminated disease. Following initial treatment, infants with CNS or disseminated disease may also receive a six-month course of oral suppressive acyclovir to prevent recurrences and improve neurodevelopmental outcomes.