Researchers have learned a lot this year about the severe damage Zika virus can cause to the developing fetus, but many questions remain, said Margaret Honein, MPH, PhD, chief of Centers for Disease Control and Prevention (CDC)’s Birth Defects Branch in the National Center on Birth Defects and Developmental Disabilities.
“If a woman is infected, does she have a 1% risk, a 25% risk or some other level of risk of having a baby affected by a major birth defect?” she asked her audience of CDC’s Epidemic Intelligence Service officers and other public health professionals at a special session on Zika virus infection during the 65th Annual EIS Conference in Atlanta, Georgia.
“We don’t know when during pregnancy the Zika virus infection poses the highest risk to the fetus, although based on other viral infections and the preliminary evidence, we expect that it will be during the first and early in the second trimester. We don’t know the full range of potential health problems that Zika virus infection can cause, and we don’t know what other factors, such as co-occurring infections, might impact the risk of birth defects,” she said.
After evaluating the epidemiologic, clinical, lab and pathological evidence, though, based on Shepherd’s criteria for teratogens and the Bradford Hill criteria for causation, the CDC concludes that Zika virus causes microcephaly
and other brain anomalies, Dr. Honein noted.
Dr. Honein updated the audience about what researchers have learned about the impact of Zika infection on pregnant women and their babies. The updates are listed below:
- A woman can be infected through a mosquito bite or sex with an infected partner. If she is infected near the time of conception, during her pregnancy or near birth, Zika can be passed to her child, with devastating outcomes.
- Infection can occur during any trimester and pregnant women do not seem to have increased susceptibility to Zika virus compared with the general population. Zika virus infection incidence in pregnant women is unknown, but they don’t seem to be more severely infected than other people.
- Zika virus infection has been detected in fetal brain tissue, amniotic fluid, placenta, and products of conception from pregnancies of women infected with Zika and in brains of newborns with microcephaly that show severely smaller volume, scattered intracranial calcification and large ventricles.
- Researchers think severe microcephaly may be due to fetal brain destruction sequence leading to fetal skull collapse, microcephaly, neurological impairment, and excess scalp skin.
- The babies may have eye abnormalities, hearing and swallowing impairments, seizures, hypertonicity contractures including clubfoot, severe irritability, growth retardation, and they may die in utero or be spontaneously aborted.
- The link between Zika and microcephaly in newborns was first recognized in fall, 2015 in Brazil after a Zika virus outbreak there was followed by more babies born with microcephaly. In Brazil, 29% of 42 women with lab-confirmed Zika virus infection had fetuses with abnormalities on prenatal ultrasound and 2 fetuses died; 17% of those with abnormalities had structural brain abnormalities including microcephaly, intracranial calcification and brain atrophy. Many of these pregnancies are still ongoing, Dr. Honein mentioned, so they haven’t been confirmed postnatally.
- In a recent case report from the United States, a woman who traveled during her first trimester of pregnancy to areas with active Zika virus transmission reported Zika-like symptoms during her 12th week of gestation. Her initial prenatal ultrasounds were normal and did not detect microcephaly, but between weeks 16 and 20, her fetus showed decreased head circumference and significant intracranial abnormalities, including cerebral atrophy. An autopsy of the fetus after an elective abortion showed cerebral cortical thinning and high levels of Zika virus in the brain and other tissues.
Dr. Honein invited CDC’s EIS officers to join the agency’s “historic response” in the fight against Zika.
Lorraine L. Janeczko, MPH, is a medical science writer who creates news, continuing medical education and feature content in a wide range of specialties for clinicians, researchers and other readers. She has completed a Master of Public Health degree through the Department of Epidemiology of the Johns Hopkins Bloomberg School of Public Health and a Dana Postdoctoral Fellowship in Preventive Public Health Ophthalmology from the Wilmer Eye Institute, the Johns Hopkins University School of Medicine and the Bloomberg School.
SOURCE: EIS 2016 Conference Program, p 29: Zika Virus and Pregnant Women: Adverse Pregnancy Outcomes
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