Fetal effects unclear: watch for West Nile virus in pregnancy.(News)

ATLANTA -- The Centers for Disease Control and Prevention is asking clinicians to be on the alert for cases of possible. West Nile virus in pregnant women this summer, as investigators attempt to determine the effects of intrauterine exposure.

Congenital infection does occur, but the proportion of infected pregnant women who transmit West Nile virus to their fetuses is unknown and the effects of the virus on the fetus are unclear, Dr. Ned Hayes said at the International Conference on Emerging Infectious Diseases.

The first five cases of congenital West Nile virus infection were seen in 2002. Three of the affected infants, while serologically positive, appeared to be normal, Dr. Hayes said.

One baby was severely infected, having positive IgM and RNA in the cord tissue and placenta. The infant, who died, had cystic cerebral tissue destruction and severe chorioretinitis. The fifth case was a published report of maternal infection, but the infant was not tested (Obstet. Gynecol. 102[2]:229-31. 2003).

The infant who died clearly was infected and had congenital abnormalities, but causality has not been established definitively, Dr. Hayes said.

Flavivirus infection in pregnancy has been associated with spontaneous abortion and neonatal infection, but has not been known to cause birth defects. West Nile virus is a single-stranded RNA flavivirus.

"During 2003 we intensified surveillance, identifying 72 cases of West Nile virus infection in pregnant women," he said. Most occurred in the western and north central states hardest hit that year.