Mom's symptomless herpes threatens baby.

Herpes can be deadly for newborns who acquire the viral infection from their mothers during labor or delivery. To complicate matters, only about 25 percent of adults with genital herpes display telltale symptoms (SN:6/28/86, p.410). Seattle-based researchers have now tested a group of mothers during labor for asymptomatic but infectious herpes, and have reached some disturbing conclusions. Their data suggest that such screening will neither identify all women who risk passing the virus to their newborns, nor allow physicians to save infected babies from a devastating outcome.

Zane A. Brown and his co-workers at the University of Washington identified 56 women with active, asymptomatic herpes infections among the 15,923 laboring women tested at two local hospitals between 1984 and 1989.

Type 1 herpesvirus, the "oral" form usually associated with cold sores, rarely infects the genitalia. However, says Brown, "our data indicate that when it is present [in the genitalia], it transmits more readily [than Type 2] to infants." Three of the five women (60 percent) with Type 1 herpes infected their babies, compared with seven of the 51 women (14 percent) with active Type 2 herpes, the researchers report in the May 2 NEW ENGLAND JOURNAL OF MEDICINE.

The Type 1 infection almost never harms a newborn, Brown observes. In his study, all infants contracting Type 1 herpes developed normally. By contrast, one of the seven infants with Type 2 herpes died, and four developed disabling encephalitis.

"The really big risk of neonatal infection and damage or death occurs if a woman first acquires [Type 2] herpes late in her pregnancy," Brown says. And fully one-third of the mothers with asymptomatic herpes in this study were experiencing their first, or "primary," episode of this periodically recurring disease, he adds. Although the infected infants were identified within 24 hours of birth -- far earlier than usual -- and immediately treated with antiviral drugs, "we didn't significantly change the ultimate outcome," Brown says. "Kids with Type 2 disease got sick no matter what we did."

He notes another unsettling finding: Unlike most adults, infants carrying antibodies to the Type 1 virus did not contract a milder-than-normal version of the Type 2 disease.

Fortunately, the more serious, Type 2 virus "transmits reluctantly," Brown concludes. But transmission may occur in unexpected ways. He and his colleagues speculate that in eight of the babies with herpes infections, physicians may have unwittingly opened a portal for the virus by inserting electrodes into the fetus' scalp to monitor prenatal heartbeats.