Neonatal Herpes Simplex Virus: Prophylaxis and Acyclovir Treatment

Neonatal herpes simplex virus (HSV) infection is uncommon, yet it can progress rapidly and cause permanent neurological injury or death. The two principal pathogens, HSV-1 and HSV-2, may be transmitted during labor and delivery when an infant contacts infected genital secretions. Transmission can also occur after birth through contact with an active orolabial lesion.

Clinical recognition is difficult because many affected newborns initially appear well. Skin lesions may be absent, and fever is not always present. A careful maternal history, attention to delivery circumstances, and a low threshold for diagnostic testing are therefore central to safe perinatal care.

Prevention begins before birth, continues through delivery planning, and extends into the neonatal period. When infection is suspected, intravenous acyclovir should be started promptly while laboratory investigations are underway rather than delayed until every result is available.

How Perinatal HSV Is Transmitted

The greatest transmission risk occurs when a mother acquires a first genital HSV infection close to delivery. She may have a high viral load and no established protective antibodies to pass to the fetus. Recurrent genital herpes generally carries a lower risk because maternal antibodies offer partial protection, although transmission remains possible.

A history of genital lesions, prodromal burning, or a positive HSV test should be documented during pregnancy. Suppressive maternal therapy with oral acyclovir or valacyclovir is commonly offered from around 36 weeks to people with recurrent genital herpes. This approach reduces clinical recurrences and the need for cesarean delivery, but it does not eliminate viral shedding or neonatal infection.

Delivery management depends on whether lesions or prodromal symptoms are present at labor. Cesarean delivery is generally recommended when active genital lesions or prodrome are identified, while vaginal delivery may be appropriate when there are no lesions or symptoms. Invasive fetal monitoring, artificial rupture of membranes, and prolonged rupture should be avoided when feasible because they can increase opportunities for viral exposure.

Prenatal care also relies on distinguishing infectious risks from unrelated fetal findings. For broader context on structured prenatal assessment, clinicians can review fetal screening guidance, while remembering that fetal echocardiography does not diagnose or exclude neonatal HSV.

Recognizing Disease in the Newborn

Neonatal HSV is usually classified as skin, eye, and mouth disease; central nervous system disease; or disseminated disease. These categories can overlap. A newborn with vesicles may have disease limited to the skin, yet central nervous system involvement can develop later. Conversely, severe disseminated infection may begin with nonspecific findings and no visible lesions.

Symptoms often appear between the fifth and fourteenth days of life, though onset can occur earlier or much later. Warning signs include poor feeding, lethargy, irritability, temperature instability, apnea, seizures, respiratory distress, jaundice, coagulopathy, and unexplained shock. Clusters of vesicles on the skin, scalp, eyes, or mouth are highly suggestive, but their absence must not reassure clinicians when the overall presentation is concerning.

Evaluation commonly includes HSV PCR or culture from surface sites, a blood HSV PCR, cerebrospinal fluid (CSF) analysis with HSV PCR, liver enzymes, complete blood count, renal function, and coagulation studies. Sampling surface sites at approximately 24 hours of age can help distinguish contamination from replication. If symptoms suggest encephalitis or disseminated infection, lumbar puncture and blood testing should be pursued as soon as clinically safe.

A negative early test does not always end the evaluation. Repeat CSF PCR may be needed when neurological symptoms persist, when the first specimen was obtained very early, or when clinical suspicion remains high. Consultation with neonatology, pediatric infectious disease, and neurology can help coordinate testing and treatment.

Choosing Acyclovir Treatment

Intravenous acyclovir is the standard initial therapy for suspected or confirmed neonatal HSV. The usual neonatal dose is 20 mg/kg per dose administered intravenously every eight hours, providing 60 mg/kg per day. Dosing intervals and monitoring require adjustment for prematurity, reduced renal function, and changing postnatal age.

Therapy should begin as soon as possible in an infant with a compatible illness or significant exposure. Waiting for vesicles, PCR confirmation, or deterioration can allow viral replication to reach the brain, liver, lungs, and other organs. Acyclovir is generally well tolerated, but clinicians should monitor serum creatinine, urine output, hydration, and blood counts because nephrotoxicity and neutropenia can occur.

Treatment duration is determined by disease category and response rather than by symptoms alone. Skin, eye, and mouth disease generally receives 14 days of intravenous therapy when dissemination and CNS infection have been excluded. CNS or disseminated infection requires at least 21 days, with repeat CSF HSV PCR near the end of therapy. If the CSF PCR remains positive, treatment should continue with additional testing until viral clearance is documented.

Topical treatment alone is inadequate for neonatal HSV. Eye involvement requires ophthalmology assessment, and bacterial sepsis, enterovirus, meningitis, and other causes of neonatal deterioration may require parallel treatment while the diagnostic picture develops.

Postnatal Prevention and Suppression

Postnatal exposure prevention depends on practical infection-control measures. Anyone with an active cold sore should avoid kissing the newborn, cover lesions, perform meticulous hand hygiene, and avoid direct contact between the lesion and the infant. A breastfeeding parent with a lesion on the breast should not nurse from that affected side until it has healed; expressed milk from the unaffected breast may be considered if safe handling is possible.

Parents and caregivers should be taught to report vesicles, poor feeding, unusual sleepiness, fever or hypothermia, breathing changes, and abnormal movements immediately. These instructions matter after discharge because neonatal HSV may emerge after an initially uneventful birth hospitalization.

After a completed course for neonatal HSV disease, suppressive oral acyclovir is usually prescribed for six months. A commonly used regimen is 300 mg/m² per dose by mouth three times daily, adjusted as the child grows and according to specialist guidance. Suppression reduces recurrent mucocutaneous disease and may support better neurodevelopmental outcomes in infants with CNS infection, but it does not replace developmental surveillance.

Neutropenia is a recognized adverse effect of prolonged oral acyclovir. A complete blood count is therefore monitored during suppression, particularly early in the course or when the infant is medically fragile. Families should receive clear instructions about dosing, missed doses, side effects, and the importance of continuing therapy until the planned review.

Exposure Management Without Symptoms

An asymptomatic infant born to a mother with genital lesions requires a risk-based evaluation. The management differs according to whether the maternal infection is likely to be a first episode, a nonprimary first episode, or a recurrent infection. Maternal type-specific serology, lesion testing, previous history, and timing of symptoms may help clarify the category.

For some infants born by cesarean delivery before membrane rupture to a mother with recurrent lesions, clinicians may favor observation with virologic testing rather than immediate treatment. In other situations—especially a suspected primary maternal infection near delivery, prolonged rupture of membranes, or positive infant testing—evaluation and empiric intravenous acyclovir are more likely to be appropriate.

There is no universal “prophylaxis” course for every exposed newborn. Unnecessary acyclovir exposes infants to intravenous access, renal monitoring, and medication toxicity, while undertreatment can be disastrous. Decisions should follow a current neonatal HSV pathway and involve pediatric infectious disease expertise when the maternal history or delivery details are uncertain.

The timing of testing also matters. Surface specimens and blood PCR may be collected according to local protocol, and a lumbar puncture is indicated when infection is confirmed or when symptoms raise concern for CNS involvement. An infant who develops symptoms during observation should be treated as a possible case, not merely as an exposed but well newborn.

Practical Priorities for Clinical Teams

The most reliable systems combine prenatal counseling, delivery-room communication, rapid laboratory access, and clear discharge instructions. Hospitals should ensure that obstetric and neonatal teams can quickly identify maternal lesion status, membrane duration, delivery mode, antiviral exposure, and the infant’s examination findings.

Teams preparing educational or scientific resources on perinatal medicine can also use the FAOPS 2020 congress archive as background on the professional setting in which neonatal and perinatal research is discussed. Clinical decisions, however, should rely on current guidelines and local antimicrobial stewardship policies because recommendations and testing availability may change.

• Ask about maternal genital or oral HSV history early and again at labor.
• Start intravenous acyclovir promptly when neonatal HSV is clinically suspected.
• Obtain surface, blood, CSF, and liver-related investigations according to the presentation.
• Adjust dosing and monitoring for renal function, prematurity, and treatment duration.
• Arrange six months of suppressive therapy and developmental follow-up after neonatal disease.

Neonatal HSV demands coordinated action because the window between subtle illness and organ injury can be short. Prevention lowers exposure risk, but rapid recognition and correctly dosed acyclovir remain essential safeguards. Clinical teams should review their local neonatal HSV pathway, confirm access to PCR testing and intravenous therapy, and educate families before discharge so that concerning symptoms trigger immediate assessment.