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A hallmark of infection with the mosquito-borne Zika virus in pregnant women is delivering a baby with an abnormally small head -- a condition called microcephaly. But as children exposed to Zika in the womb are growing up, researchers are learning that it's not only the youngsters born with microcephaly that they need to worry about.
"Zika virus-exposed infants without microcephaly who may appear normal at the time of birth may have other abnormalities present at higher frequencies than what would be expected in the general population," said study author Jessica Cranston. She's a third-year medical student at the David Geffen School of Medicine at the University of California, Los Angeles.
Cranston said it's important to monitor children who've been exposed to Zika to ensure that they grow normally and meet their developmental milestones. By doing so, doctors can detect problems early and offer interventions to potentially improve a child's development.
Right now, there is no known transmission of Zika virus in the United States. But there were reports of Zika infections in Florida and Texas in 2016 and 2017, according to the U.S. Centers for Disease Control and Prevention. Other countries, including Brazil, experienced significant Zika outbreaks in 2015 and 2016.
Zika virus is transmitted through mosquito bites. People who get infected may not have any symptoms, or they may have mild symptoms. Possible symptoms include fever, rash, headache, joint pain, red eyes and muscle pain. In pregnant women, however, the Zika virus can lead to microcephaly and other brain and birth defects in babies.
The new study included data on nearly 300 infants with known (74%) or suspected Zika infections acquired during pregnancy. Twenty-four percent of the children were born with microcephaly. The rest appeared to have normally developed heads.
The babies' health and development was followed from December 2015 to July 2019. Children received monthly evaluations during the first six months of life. After the first six months, children were evaluated every three months.
The researchers found that head circumference varied over time for some of the children. In babies born with a normal head size, about 10% developed microcephaly during the follow-up. Conversely, 7.5% of those born with microcephaly went on to have a normal head size during the study.
Neurological exams were performed on 213 of the infants. Seventy-five percent had abnormal findings, such as overactive reflexes. In youngsters with microcephaly, 26% had hearing problems and 79% had eye abnormalities. The children with normally sized heads didn't escape having hearing or eye issues -- 10% had hearing problems and 18% had eye abnormalities. Some children also experienced trouble with growing as expected and some had difficulty swallowing.
Imaging tests were done on 203 children. Ninety-six percent of those with microcephaly had abnormal findings on these tests compared to 29% of those with normally sized heads.
The bottom line, said Cranston, is that infants born without obvious symptoms shouldn't be dismissed as unaffected.
"These infants should be followed closely during the first few years of their lives to monitor for any developmental delay," she said.
The study was published online July 7 in JAMA Network Open.
Dr. Sarah Mulkey, director of fetal, transitional and neonatal neurology fellowship at Children's National Hospital in Washington, D.C., wasn't involved in the latest research, but wrote an editorial accompanying the new study. Mulkey has also conducted research on children born with Zika who appeared to be normal at birth, but later developed neurological issues.
"Initially, we were seeing kids born with obvious birth defects like microcephaly. What we're now learning is that there is a spectrum of other clinical outcomes. If you had Zika and your child was born without any birth defects, it's very important to maintain developmental follow-up through school age," she explained.
Mulkey said it's crucial to have your child's head circumference measured regularly (this is something most pediatricians do). Having a record of your child's head circumference allows doctors to make sure the brain is developing as it should.
Mulkey noted that the latest findings suggest that "even a low-normal finding may be an indication of a need for neurodevelopmental follow-up."
She also said that many Zika infections in pregnancy may have gone undiagnosed. If a child is born without an obvious defect, more subtle neurological problems or developmental issues related to Zika may go undetected. Mulkey said the children with obvious defects are likely just "the tip of the iceberg."
If you lived in or traveled to an area where Zika was present while you were pregnant, Mulkey said to make sure your child's pediatrician knows so that they can perform neurodevelopmental screening exams to ensure that your youngster is reaching important developmental milestones.
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