How Can Babies Get Neonatal HSV Without Genital Herpes?

Many parents are shocked and overwhelmed to learn their baby has neonatal herpes simplex virus (HSV), especially when the mother has never had a diagnosed case or history of genital herpes. It is a very common misconception that a mother must have a history of genital herpes for her baby to contract the virus. In fact, in a major UK and Ireland surveillance study, over 80% of babies who developed neonatal HSV had mothers with no known history of genital herpes ^[1].

Because the virus can be shed without symptoms, and because cold sores are incredibly common, transmission is often completely undetectable before it happens ^[2][3]. Learning how your baby might have contracted HSV can help you understand their condition, but it should never be a source of blame or guilt. The exact source and timing are often impossible to determine.

There are three main timeframes when a baby can be exposed to HSV, even when the mother has no history of genital herpes:

1. During Delivery (Peripartum Transmission)

This is the most common route, accounting for about 85% of neonatal HSV cases ^[4]. A baby can contract the virus while passing through the birth canal if the mother has an active genital infection. This can happen in two ways when a mother has no prior history:

• Asymptomatic Shedding: The herpes virus can be actively replicating and present on the skin or mucosal surfaces (like the birth canal) even when there are no visible sores or symptoms ^[2]. A person can carry the virus for years without a noticeable outbreak, yet still pass it during delivery ^[5].
• Newly Acquired Infection: A mother might contract genital herpes for the first time during pregnancy from a partner, including through oral sex from a partner with a history of oral cold sores (HSV-1) ^[6]. The highest risk to the baby occurs if the mother acquires a primary infection (first-ever HSV infection) near the time of delivery ^[7]. In this specific scenario, the risk of transmission during vaginal delivery can be between 25% and 44%, because the mother has not yet produced protective antibodies (immune system proteins that fight the virus) to pass to the baby ^[7][8]. For comparison, the transmission risk from a long-standing, recurrent maternal infection is much lower (about 1%) because the mother’s antibodies provide some protection ^[7][9].

2. After Birth (Postnatal Transmission)

Around 10% of cases are contracted after the baby is born ^[4]. This typically occurs through direct contact with an infected caregiver, relative, or visitor.

• HSV-1 (the virus that causes cold sores) can be transmitted if someone kisses the baby or if the baby comes into direct contact with a cold sore or infected saliva ^[10].
• The virus can sometimes be shed in saliva even when no cold sore is visible ^[3]. However, transmission requires direct physical contact with infectious secretions; you cannot catch it just from being in the same room.
• Prevention: To protect newborns, anyone with an active or recent cold sore should not kiss the baby, must practice strict handwashing, and should cover any lesions ^[11][6].

3. Before Birth (Intrauterine Transmission)

In very rare cases (about 5%), the virus can cross the placenta and infect the baby before labor begins ^[4].

Moving Forward: Urgent Treatment and Care

When neonatal HSV is suspected, medical teams do not wait for test results to begin treatment. Because the infection can progress quickly and cause severe damage, doctors will immediately start intravenous (IV) antiviral medication (medicine delivered directly into a vein, such as acyclovir) ^[6][12]. Specialized tests, such as PCR (polymerase chain reaction, a test that detects the virus’s genetic material), are run simultaneously on blood, cerebrospinal fluid, and swabs from the skin, eyes, or mouth to confirm the diagnosis and determine the extent of the infection ^[13][2]. The type of virus (HSV-1 vs. HSV-2) and which organs are involved will help guide your baby’s long-term care and follow-up.

Urgent Warning Signs at Home

Neonatal HSV does not always cause visible skin blisters ^[1]. If your baby has been exposed or if you have been discharged, seek emergency medical care immediately if you notice:

• Fever (38°C/100.4°F or higher) or low body temperature ^[14]
• Poor feeding or extreme sleepiness (lethargy) ^[12]
• Unusual irritability ^[14]
• Any new blisters, sores, or eye redness ^[12]
• Difficulty breathing or seizures ^[12][14]

A Note on Finding the Source

The self-reflection questions below are optional clues that may help the clinical team, but they are not a way to prove who was responsible. Blood tests on parents can show past exposure to HSV, but they usually cannot tell exactly when or from whom the virus was acquired.