West Nile, A Pregnancy Danger?

Last Editorial Review: 2/28/2004

If a woman becomes ill with West Nile fever while she is pregnant, can her baby be damaged by the West Nile virus (WNV)? In 2002, there were 4 confirmed cases of WNV infection involving pregnant women and one baby was born with not only detectable WNV infection but also with brain damage possibly caused by the virus.

The CDC is now gathering outcome data for pregnancies of WNV-infected mothers. The CDC Guidelines include -- how to screen for WNV during pregnancy, how to diagnose WNV infection during pregnancy, evaluation of the fetus with ultrasound and possibly, tissue biopsy or amniotic fluid, and evaluation of babies after birth. The report concludes with recommendations as to how women can avoid being infected with the WNV in the first place. These same recommendations are applicable to everyone, pregnant or not.

Barbara K. Hecht, Ph.D.
Frederick Hecht, M.D.
Medical Editors, MedicineNet.com

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Interim Guidelines for the Evaluation of Infants Born to Mothers Infected with West Nile Virus During Pregnancy

West Nile virus (WNV) is a single-stranded RNA flavivirus with antigenic similarities to Japanese encephalitis and St. Louis encephalitis viruses. It is transmitted to humans primarily through the bites of infected mosquitoes. Flavivirus infection during pregnancy has been associated rarely with both spontaneous abortion and neonatal illness but has not been known to cause birth defects in humans (1--4). During 2002, a total of 4,156 cases of WNV illness in humans, including 2,946 cases of neuroinvasive disease, were reported to CDC by state health departments. In 2002, a woman who had WNV encephalitis during the 27th week of her pregnancy delivered a full-term infant with chorioretinitis, cystic destruction of cerebral tissue, and laboratory evidence of congenitally acquired WNV infection (5,6). Although this case demonstrated intrauterine WNV infection in an infant with congenital abnormalities, it did not prove a causal relation between WNV infection and these abnormalities. During 2002, CDC investigated three other instances of maternal WNV infection. In all three cases, the infants were born at full term with normal appearance and negative laboratory tests for WNV infection; cranial imaging studies and ophthalmologic examinations were not performed. During 2003, CDC received reports of approximately 9,100 cases of WNV illness, including approximately 2,600 cases of neuroinvasive disease*. CDC is gathering data on pregnancy outcomes for approximately 70 women with WNV illness during pregnancy (CDC, unpublished data, 2003).

To develop guidelines for evaluating infants born to mothers who acquire WNV infection during pregnancy, on December 2, 2003, CDC convened a meeting of specialists in the evaluation of congenital infections. This report summarizes the interim guidelines established during that meeting.

Screening for WNV During Pregnancy

No specific treatment for WNV infection exists, and the consequences of WNV infection during pregnancy have not been well defined. For these reasons, screening of asymptomatic pregnant women for WNV infection is not recommended.

Diagnosis of WNV Infection During Pregnancy

Pregnant women who have meningitis, encephalitis, acute flaccid paralysis, or unexplained fever in an area of ongoing WNV transmission should have serum (and cerebrospinal fluid [CSF], if clinically indicated) tested for antibody to WNV. If serologic or other laboratory tests indicate recent infection with WNV, these infections should be reported to the local or state health department, and the women should be followed to determine the outcomes of their pregnancies.

Evaluation of the Fetus in Pregnant Women with WNV Infection

If WNV illness is diagnosed during pregnancy, a detailed ultrasound examination of the fetus to evaluate for structural abnormalities should be considered no sooner than 2--4 weeks after onset of WNV illness in the mother, unless earlier examination is otherwise indicated. Amniotic fluid, chorionic villi, or fetal serum can be tested for evidence of WNV infection. However, the sensitivity, specificity, and predictive value of tests that might be used to evaluate fetal WNV infection are not known, and the clinical consequences of fetal infection have not been determined. In case of miscarriage or induced abortion, testing of all products of conception (e.g., the placenta and umbilical cord) for evidence of WNV infection is advised to document the effects of WNV infection on pregnancy outcome.

Evaluation of Infants Born to Mothers Infected with WNV During Pregnancy

When an infant is born to a mother who was known or suspected to have WNV infection during pregnancy, clinical evaluation is recommended (Box 1). Further evaluation should be considered if any clinical abnormality is identified or if laboratory testing indicates that an infant might have congenital WNV infection (Box 2).

Prevention of WNV Infection During Pregnancy

Pregnant women who live in areas with WNV-infected mosquitoes should apply insect repellent to skin and clothes when exposed to mosquitoes and wear clothing that will help protect against mosquito bites. In addition, whenever possible, pregnant women should avoid being outdoors during peak mosquito-feeding times (i.e., usually dawn and dusk).

Reported by: E Hayes, MD, D O'Leary, DVM, Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases; SA Rasmussen, MD, Div of Birth Defects and Developmental Disabilities, National Center on Birth Defects and Developmental Disabilities, CDC.

Source: Center for Disease Control (cdc.gov)


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