New estimate shows frequency of Zika-associated birth defects in US
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According to a new estimate published in MMWR, around 5% of U.S. infants born to mothers with a confirmed or possible Zika virus infection during pregnancy had a Zika-associated brain or eye defect, and many had more than one.
The estimate is based on data from nearly 6,800 births that occurred in the U.S. and its territories from December 2015 through March 2018 and were reported to the U.S. Zika Pregnancy and Infant Registry (USZPIR).
The 2015-2016 Zika virus epidemic was centered on Brazil, but widespread local transmission also occurred in Puerto Rico and the U.S. Virgin Islands. On the U.S. mainland, Florida and Texas both reported local transmission.
According to the CDC, there has not been a locally acquired case of Zika virus in a U.S. state since 2017, although they continue to occur in U.S. territories. Zika is spread mainly through the bite of infected Aedes species mosquitoes.
The new MMWR report is the first to describe Zika-associated birth defects from the USZPIR “with data combined from the U.S. states, D.C., and U.S. territories and freely associated states,” the authors said. It describes not only the frequency of birth defects overall but also the most commonly reported defects.
Among the 6,799 births reported to the USZPIR during the study period, 4.6% of infants born to women with confirmed or possible Zika virus infection during pregnancy had a Zika-associated brain or eye defect. The frequency was higher — 6.1% — in a subgroup of pregnancies in which the mother’s infection was confirmed by nucleic acid amplification testing.
Around 35% of infants with a birth defect — 110 out of 315 — had more than one defect. Several brain and eye defects occurred more frequently, including microcephaly, corpus callosum abnormalities, intracranial calcification, abnormal cortical gyral patterns, ventriculomegaly, cerebral or cortical atrophy, chorioretinal abnormalities and optic nerve abnormalities, the researchers reported.
“These findings can help target surveillance efforts to the most common brain and eye defects associated with Zika virus infection during pregnancy should a Zika virus outbreak reemerge, and might provide a signal to the reemergence of Zika virus, particularly in geographic regions without ongoing comprehensive Zika virus surveillance,” the authors wrote.
References:
CDC. Zika cases in the United States. https://www.cdc.gov/zika/reporting/index.html. Accessed Jan. 21, 2022.
Roth NM, et al. MMWR Morb Mortal Wkly Report. 2022;doi:10.15585/mmwr.mm7103a1.
Perspective
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Much has been learned in the past 6 years since the beginning of the Zika virus epidemic. We now have a better understanding of the range of birth defects that can be seen and the impact on child neurodevelopment. Despite Zika not being at the forefront of the current news, we need to continue to learn and understand how this virus may affect pregnancies so we can detect a reemergence if and when it occurs.
In this MMWR report of infants born to pregnant women with possible or confirmed Zika virus infection in pregnancy in U.S. states and territories, Zika-associated brain or eye birth defects were seen in about 5% of infants. As in other studies, the risk was higher for infections that occurred at earlier gestational ages, but the risk was not different for women with or without symptoms.
Although some of the brain abnormalities are more specific to Zika virus, such as microcephaly and subcortical calcifications, many of these brain abnormalities are nonspecific. For example, microcephaly and ventriculomegaly can be seen in other congenital infections, such as cytomegalovirus infection, and can also be seen in genetic syndromes. Abnormalities of the corpus callosum can also have a variety of etiologies, many of which are noninfectious. Similarly, some of the eye abnormalities can be seen because of various underlying causes and may not relate to a congenital infection. When considering a congenital infectious etiology, Zika virus is certainly on the list.
It is important to continue to consider Zika virus in the differential diagnosis of congenital abnormalities of the brain and eye. Physicians caring for pregnant women should continue to ask about travel history if outside of a geographic region where Zika virus may circulate. When a pregnancy is identified that has an abnormal fetal brain finding, testing for Zika virus if there is an epidemiological link to potential exposure should be considered. In infants with microcephaly or other birth defects, neuroimaging and ophthalmology examination remain an important part of the infant evaluation. Long-term neurologic and developmental follow-up is needed for all infants with antenatal Zika virus exposure to identify and treat any neurodevelopmental delays.
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