In the majority of cases, West Nile virus is spread to humans by infected mosquitoes, and although viruses in the family Flaviviridae have been associated on occasion with neonatal illness and spontaneous abortion, until 2002 they hadn't been associated with birth defects. At that time, a woman who had developed West Nile virus-associated encephalitis while pregnant gave birth to an infant who tested positive for the virus and had congenital cerebral abnormalities; three other infants born to other mothers infected with West Nile virus appeared normal and were not infected, although not all appropriate tests were performed. In December 2003 the Centers for Disease Control and Prevention (CDC) called together congenital infectious disease experts to formulate guidelines on evaluating infants of women who contract West Nile virus during pregnancy.
The CDC recommends screening for West Nile virus in pregnant women who develop meningitis, encephalitis, acute flaccid paralysis, or unexplained high fever if they live in an area in which the virus has been found. Blood and, if indicated, cerebrospinal fluid testing should be performed.
If West Nile virus is diagnosed during pregnancy, fetal ultrasonography should be performed after the onset of illness (and no sooner) to assess for structural abnormalities. In cases of induced or spontaneous abortion, all products of conception should be analyzed for viral infection. An infant born to a woman with suspected or confirmed infection should undergo a comprehensive includes evaluation for neurologic, ophthalmologic, splenic, hepatic, or skin abnormalities; a hearing evaluation; and testing for serum immunoglobulin M and immunoglobulin G antibodies. The placenta should be examined by a pathologist and specimens retained for subsequent evaluation.
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All pregnant women should be instructed to take preventive measures, such as wearing long sleeves and pants, using insect repellent containing DEET on skin and clothing when exposure is anticipated, and avoiding mosquito-infested areas, especially at dawn and dusk.
MMWR Morb Mortal Wkly Rep 2004;53(7):154-7.