A baby can contract the herpes simplex virus (HSV), a condition known as Neonatal Herpes Simplex Virus infection. While rare, occurring in an estimated 1 in 3,200 deliveries, it carries significant potential for serious health consequences for the newborn. Neonatal HSV is caused by the same virus responsible for common cold sores (HSV-1) and genital herpes (HSV-2). Because a newborn’s immune system is still developing, the virus can spread quickly and cause severe disease if not identified and treated immediately.
Understanding Transmission Routes
The vast majority of neonatal HSV cases are acquired during the birthing process, known as perinatal transmission. This occurs when the infant passes through the birth canal and comes into direct contact with active genital lesions or the virus shed in maternal genital secretions. This route accounts for approximately 85% of all neonatal infections, even if the mother has no visible symptoms at the time of delivery.
An infant can also contract the virus after birth, classified as postnatal transmission. This happens when a newborn is exposed to the virus from a caregiver, such as the mother, who has an active lesion like a cold sore. Postnatal transmission accounts for about 10% of cases and often occurs through close contact, such as kissing or touching the baby. Caregivers with cold sores must exercise strict hygiene to prevent viral transfer.
The rarest route is congenital transmission, which occurs in utero when the virus crosses the placenta to infect the fetus during pregnancy. This accounts for the remaining 5% of neonatal HSV infections. Infection at this stage is possible with both primary and recurrent maternal infections, but it is an uncommon event.
Risk Levels Based on Maternal Status
The risk of a baby contracting HSV depends heavily on the mother’s immune status and the timing of her infection. The most significant factor influencing transmission is a primary (first-ever) genital herpes infection near the time of delivery. If a mother contracts the virus late in the third trimester, she has not yet produced protective antibodies to pass to the baby. In this high-risk scenario, the transmission rate during a vaginal delivery can be as high as 30% to 50%.
If the mother has a history of genital herpes and experiences a recurrent outbreak, the risk of transmission is substantially lower. The mother’s immune system has already produced antibodies against the virus, which are transferred across the placenta to the fetus. These antibodies provide the baby with passive protection against infection. The risk of transmission from a recurrent infection is generally low, ranging from 0% to 5%.
Active genital lesions at the time of delivery significantly increase the chance of transmission. However, the virus can also be shed asymptomatically in the genital tract, meaning the mother may not realize she is infectious. Asymptomatic shedding is why up to 80% of mothers who deliver an HSV-infected infant have no known history of genital lesions. Other factors that increase the risk include prolonged rupture of membranes and the use of invasive monitoring procedures during labor.
Recognizing Symptoms in Newborns
Recognizing the signs of neonatal HSV is challenging because initial symptoms can be subtle and easily mistaken for other common newborn issues. The typical window for symptoms to appear is between the first and fourth weeks of life, though onset can occur as late as six weeks. Clinicians classify neonatal HSV into three main categories based on the extent of the infection, which informs treatment and long-term prognosis.
The mildest form is disease localized to the Skin, Eyes, and Mouth (SEM), accounting for approximately 40% to 45% of cases. This presentation involves small, fluid-filled blisters or vesicles appearing on the skin, often in clusters. Lesions can also be found in the mouth or on the eyes, although the infant may otherwise appear healthy.
The infection can also affect the Central Nervous System (CNS), representing about 30% to 35% of cases. Symptoms of CNS involvement include lethargy, irritability, poor feeding, and seizures. This form carries a high risk of long-term neurological damage, even with treatment. A localized SEM infection can rapidly progress to CNS or disseminated disease if left untreated, making timely diagnosis essential.
The most severe category is Disseminated Disease, which affects multiple internal organs like the liver, lungs, and adrenal glands, making up about 25% of cases. Infants with this form often show signs of systemic illness, such as breathing difficulties, diminished muscle tone, and problems with blood clotting. Untreated, disseminated HSV has a high mortality rate and requires immediate medical intervention.
Prevention and Medical Management
Proactive prevention strategies begin during the later stages of pregnancy for mothers with a history of genital herpes. Healthcare providers often recommend antiviral suppressive therapy, typically with Acyclovir, starting around 36 weeks of gestation. This medication helps to reduce the frequency of genital herpes recurrences and the likelihood of viral shedding at the time of delivery.
The method of delivery is a primary preventative measure if the mother has active lesions at term. An elective Cesarean section (C-section) is recommended for any woman who has an active genital outbreak or is experiencing prodromal symptoms when labor begins. Delivering the baby via C-section minimizes the infant’s exposure to the virus in the birth canal, significantly lowering the risk of transmission.
Postnatal precautions focus on preventing transmission from a caregiver with an oral lesion or cold sore. Anyone with an active cold sore should avoid kissing the baby and must practice meticulous hand hygiene before touching the infant. Mothers with a cold sore are advised to wear a disposable mask when caring for their baby until the lesion has fully crusted and dried.
If a newborn is diagnosed with HSV, immediate medical management involves administering high-dose intravenous Acyclovir. The duration of this treatment depends on the classification of the disease: localized SEM infection requires 14 days of IV therapy, while CNS or disseminated disease requires a minimum of 21 days. Following the acute IV treatment, infants with any form of neonatal HSV are typically given oral Acyclovir for six months as suppressive therapy. This long-term regimen is essential for improving neurodevelopmental outcomes and reducing the chance of neurological complications.