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Placental transfers

There are concerns that mother-to-child transmission of WNV can occur with possible adverse health effects to the fetus. There are, as yet, no statistics showing what percentage of WNV infections in the mother result in infection of the fetus. However, one case of transplacental transmission is documented. In August, 2002, a 20-year old woman developed symptoms of WNV at the 27th week of pregnancy. Two weeks later, her symptoms worsened, including weakness in both legs. The woman was diagnosed with meningoencephalitis caused by WNV. At the 38th week of pregnancy, the patient delivered a live infant with severe cerebral abnormalities, including bilateral white-matter loss in the temporal and occipital lobes and cystic change in one temporal lobe consistent with focal cerebral destruction. The infant tested positive for WNV, confirming intrauterine infection. It was not clear whether the cerebral abnormalities were caused by WNV, but it is obviously a possibility. Because of this case, the CDC increased monitoring of WNV in pregnancy.

A 2003 study of 72 WNV infected women who were pregnant showed a pattern suggesting that WNV could result in abnormalities of the fetus. Five of the women had miscarriages and 2 had elective abortions. When the study was reported, 23 had not yet delivered so there was information only about the remaining 42 live births:

No. of fetuses/infants	Outcome
28	Apparently normal at delivery
3	Condition unknown
1	Down’s syndrome
1	Lissencephaly [smooth cerebrum without convolutions]
1	Cleft palate
2	Microcephaly
3	Rash
1	Skin tags
2	Born prematurely

Note that one infant had laboratory evidence of intrauterine WNV infection without clinical illness, and 3 infants had laboratory evidence of WNV infection that could have been acquired in utero but, because of specimen timing, could not be confirmed.

The CDC continues to monitor the effects of WNV on pregnancy and the fetus. It is important that pregnant women use precautions to avoid infection with WNV. Pregnant women who think they may be infected should be advised to seek medical testing. Healthcare providers should question women who are pregnant about mosquito bites or signs of infection and provide information about methods to prevent infection as a part of routine care, especially in areas with verified WNV infections.

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Studies have shown a pattern of abnormalities in some babies born to WNV infected mothers.