Merck Manual

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Herpes Simplex Virus (HSV) Infection in Newborns

(Neonatal Herpes Simplex Virus Infection)


Brenda L. Tesini

, MD, University of Rochester School of Medicine and Dentistry

Last full review/revision Jul 2020| Content last modified Jul 2020
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Herpes simplex virus infection usually causes only annoying, recurring blisters in healthy adults but can cause severe infection in newborns.

  • Newborns may become infected at birth or after birth.

  • The main symptom is a rash of blisters.

  • The diagnosis is typically based on tests of samples taken from the blisters.

  • Many untreated children die.

  • To prevent spreading the infection, infected women may have a cesarean delivery.

  • Newborns with herpes simplex virus infection are given the antiviral drug acyclovir.

Usually, herpes simplex virus (HSV) is transmitted during delivery through the mother’s infected genital tract. Even infected mothers who do not have any symptoms of herpes can still transmit the infection. Sometimes newborns become infected after birth when the infection is spread by someone with an active infection. In newborns, HSV infection can lead to death or chronic problems.


Symptoms of herpes simplex virus infection usually start between the first and third weeks of life but rarely may not appear until the fourth week. The first symptom is usually a rash of small, fluid-filled blisters. The blisters can also appear inside the mouth and around the eyes.

Examples of Sores and Blisters in Herpes Simplex Virus Infection in Newborns

In some newborns, the infection affects only certain areas (localized). For example, the infection may involve only the eyes, skin, or mouth. Sometimes, only the brain and nervous system are affected. If localized infection is not treated, some newborns develop widespread disease.

In other newborns, the infection is widespread and affects many areas. In these infants, organs such as the eyes, lungs, liver, brain, and skin are all affected. Symptoms include sluggishness, diminished muscle tone, breathing problems, pauses in breathing (apnea), and seizures.


  • Testing of a sample taken from blisters and other body fluids

To diagnose herpes simplex virus infection, doctors take samples of material from the blisters and other body fluids and send the samples to a laboratory to grow (culture) the virus and identify the herpes simplex virus. Doctors may also do the polymerase chain reaction (PCR) test on the samples. This test looks for the genetic material of the virus and enables doctors to rapidly identify the virus.

If doctors suspect the newborn has a brain infection, a spinal tap (lumbar puncture—see figure How a Spinal Tap Is Done) to obtain a sample of spinal fluid may be done.


If herpes infection of the newborn is not treated, it usually progresses to severe problems. About 85% of babies with untreated widespread herpes infection die. About 50% of newborns with untreated brain infection die. Death is not common among newborns whose infection is limited to the skin, eyes, or mouth. Without treatment, at least 65% of survivors of widespread disease or brain infection have severe neurologic problems.

Appropriate treatment with antiviral drugs decreases the death rate and significantly increases the likelihood of normal development.


Efforts to prevent transmission from the mother to the newborn have not been very effective. However, women who have blisters on their genitals near the time of delivery should be tested for herpes simplex infection.

If women have an active herpes infection at the time of delivery, cesarean delivery (C-section) may be done to decrease the risk of transmitting the infection to the newborn. Also, fetal scalp monitors would not be used during labor on a newborn whose mother may have active genital herpes because the monitors stick into the scalp and could spread the infection. Newborns who are born to women who have an active herpes infection should be tested for herpes simplex virus infection.

When given to women during the last few weeks of pregnancy, the antiviral drugs acyclovir or valacyclovir may prevent recurrences at the time of delivery and decrease the need for cesarean delivery.


  • Acyclovir

Newborns who have a widespread infection are given the antiviral drug acyclovir by vein (intravenously) for 3 weeks and then by mouth for 6 months. Newborns who have a localized infection are given acyclovir intravenously for 2 weeks. This drug does not cure the infection but helps keep it from spreading and limits the symptoms.

Eye infections are treated with trifluridine, iododeoxyuridine, or vidarabine drops as well.

Additional care, such as fluids and breathing support, is provided as needed.

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