New Zika Virus Findings on Birth Defects Revealed

What exactly is the risk for birth defects in children born to pregnant women infected with Zika virus?

A new analysis led by researchers at the Centers for Disease Control and Prevention (CDC) provides more information towards answering this question, just as the scientific community begins to learn more about how the mosquito-borne virus affects mothers and their babies. The findings of the CDC study were published in the December 15 issue of the Journal of the American Medical Association (JAMA), and covered by Contagion the same day.

In all, the CDC researchers found that, among pregnant women in the United States with completed pregnancies and laboratory evidence of possible recent Zika infection, 6% had a fetus or infant with evidence of a virus-related birth defect. Furthermore, among women with first-trimester Zika infection, 11% had a fetus or infant with a birth defect. Perhaps, most alarmingly, of the 26 affected fetuses or infants included in the analysis, 4 had microcephaly and no reported neuroimaging, while 14 had microcephaly and brain abnormalities; the other 4 had brain abnormalities without microcephaly. The authors used data from 442 completed pregnancies reported to the US Zika Pregnancy Registry between January 15 and September 22, 2016 to derive their estimates.

At present, of course, CDC guidelines recommend Zika virus testing for women with possible exposure during pregnancy, even if they are asymptomatic. But even this level of vigilance may not be enough to ensure the health of infected mothers and their children. Indeed, in a separate commentary published on the same day by The New England Journal of Medicine (NEJM), two of the physicians involved in the CDC analysis reference the response to findings regarding infant outcomes “associated with thalidomide use and rubella infection” and call for a similar global response to Zika virus. “What is clear is that the devastating effect of [Zika virus] infection is not limited to infection early in pregnancy and that damage to the fetal brain can occur even with infection in the second and third trimesters,” they write. “These findings are sobering and emphasize the public health urgency of planning for the needs of children and families affected by the congenital Zika syndrome… Countries experiencing a major increase in the total number of children with structural birth defects need to prepare for clinical, public health, social, and educational demands.”

The physicians also note that more work needs to be done to address “the limitations of current diagnostic testing” for Zika and related complications, an issue that is highlighted by other recent findings. In the same issue of NEJM, for example, a study of a cohort of pregnant women (125 completed pregnancies) from Rio de Janeiro with laboratory-confirmed Zika virus found that among 117 live infants born to 116 women, 42% were born with “grossly abnormal clinical or brain imaging findings or both,” and 4 had microcephaly. In all, 55% of pregnancies had adverse outcomes following maternal infection in the first trimester, 52% following infection in the second trimester, and 29% following infection in the third trimester.

Additionally, a case report, also published in NEJM (on December 7), noted that in a Colombian woman with laboratory-confirmed Zika, the fetus displayed no “brain abnormalities” on scans obtained at 12 and 15 weeks gestation, and that neurosonography performed at 20, 24, and 29 weeks revealed “bilateral mild ventriculomegaly and a shortened corpus callosum.” After the baby was delivered at 37 weeks gestation (due to suspected growth restriction), “postnatal ultrasonography and MRI studies confirmed the presence of microcephaly with a thinned corpus callosum and brain atrophy with parenchymal calcifications,” the authors of the report note.

“We would hypothesize that the persistent viremia that was detected in the mother could be the result of viral replication in the fetus or placenta, which thus acts as a reservoir,” they continue. “[Therefore], persistent [Zika virus RNA] in maternal serum could be a sign of fetal infection, and thus the fetus may play a role in persistent maternal viremia.”

Based on findings such as these, the CDC researchers note in their NEJM commentary that, “even in the absence of definitive testing, infants with possible congenital [Zika virus] infection will need to be followed carefully in infancy and childhood to identify any related health consequences or disabilities and to ensure that they are receiving the best available services.”

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.