Herpes Prophylaxis in Pregnancy

Herpes simplex virus (HSV) infection in pregnancy can cause significant harm to the fetus.

Briefly:

HSV invades and replicates in neurons [nerve cells] as well as in epidermal and dermal [skin] cells. Virions [viral particles] travel from the initial site of infection to the sensory dorsal root ganglion, where latency [a period of inactivity] is established. Viral replication in the sensory ganglia leads to recurrent clinical outbreaks. These outbreaks can be induced by various stimuli, such as trauma, ultraviolet radiation, extremes in temperature, stress, immunosuppression, or hormonal fluctuations. Viral shedding, leading to possible transmission, occurs during primary infection, during subsequent recurrences, and during periods of asymptomatic viral shedding.

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HSV-1 infection is acquired by early childhood, and evidence of serologic infection with HSV-1 approaches 80% in the general adult population. Only about 30% of these individuals have clinically apparent outbreaks.

In the United States, approximately 1 out of 5 adults (21-23%) is serologically positive for HSV-2. More than one half of individuals who are seropositive do not experience clinically apparent outbreaks, but these individuals still have episodes of viral shedding and transmit the virus.

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[A] serious consequence of HSV is the transmission of the virus to a neonate by a mother who is infected. Asymptomatic maternal shedding occurs approximately 7% of the time and is responsible for most neonatal HSV infections. HSV infections in neonates are most commonly due to HSV-2 and most are acquired peripartum [around the time of delivery], although in utero and postpartum [after delivery] transmission also occur. Transmission is estimated to occur at a rate of 1 case in 3500-5000 deliveries in the United States. Neonatal infection can cause long-term sequelae and rarely death.

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HSV-2 infection in pregnancy can have devastating effects on the fetus. Neonatal HSV usually manifests within the first 2 weeks of life and clinically ranges from localized skin, mucosal, or eye infections to encephalitis [brain], pneumonitis [lung], disseminated infection, and demise.

Factors that increase the risk of transmission from mother to baby include the type of genital infection at the time of delivery (higher risk with active primary infection), prolonged rupture of membranes, vaginal delivery, and an absence of transplacental antibodies. The mortality rate is extremely high (>80%) if untreated.

The problem for pregnant women is that up to 70% of all cases of neonatal herpes transmission are in women who shed HSV asymptomatically near the time of delivery.

The good news:

Women with a history of genital herpes or a primary herpes episode experienced a reduction in both subclinical and active disease recurrence when treated prophylactically with valacyclovir [500 mg po twice a day] from 36 weeks' gestation until delivery.

As a result, these women underwent fewer cesarean sections for active disease, and showed less laboratory evidence of subclinical infection on culture and polymerase chain reaction (PCR) tests.

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Among women treated with valacyclovir, ther was a 69% reduction in the rate of C-sections performed because of the presence of HSV (4% in the valacyclovir group versus 12.5% in the placebo group).

The valacyclovir group also had a lower percentage of women with active HSV, compared with the placebo group (3% vs. 12%). Both groups had a 1% incidence of prodromal symptoms.

Among the women who participated, 2% in the valacyclovir group and 9% in the placebo group were positive for HSV on culture. On PCR, 7% of the valacyclovir group and 22% of the placebo group tested positive.

None of the newborns had positive neonatal HSV cultures. Obstetric outcomes, laboratory findings, and adverse events were similar in both groups, Dr. Sheffield said.

The results suggest that 15 women would need to be treated to prevent one maternal culture that's positive for HSV, 11 women would need to be treated to prevent one C-section for HSV, and 7 women would need to be treated to prevent one positive maternal PCR test for HSV.

If you are pregnant and have a history of genital herpes (or a primary episode) please make sure to discuss HSV prophylaxis with your Ob/Gyn.