Babies from Colombia who were born healthy after being exposed to the Zika virus in the womb showed signs of neurodevelopmental delays by 18 months of age, a small study finds. The work supports long-term follow-up of babies whose mothers had the viral infection during pregnancy, the researchers say.

As a group, the 70 babies exposed to Zika didn’t hit certain developmental milestones for movement and social interaction around the times expected for healthy, nonexposed babies of the same age, researchers report January 6 in JAMA Pediatrics.

Overall, the children lagged in mobility skills such as rolling over or sitting up, and in play skills like peekaboo and searching for an object that has dropped out of sight, says Sarah Mulkey, a fetal neonatal neurologist at Children’s National Hospital in Washington, D.C. Within the group, some children developed as expected, some showed obvious development delays, and some showed more subtle delays that caregivers might not have noticed.

Because there was variability between individuals, “looking at a population enables one to see overall trends,” says neurologist Ken Tyler of the University of Colorado School of Medicine in Aurora, who was not involved in the research. “We need to aggressively follow all children whose mothers were exposed to Zika during pregnancy to understand the nature of their neurological delays.”

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Mulkey and her team, including researchers in Colombia, assessed babies born between August 1, 2016, and November 30, 2017 — during and after the Zika epidemic that gripped Brazil, Colombia and other countries in the Americas (SN: 10/30/17). About five to 10 percent of babies born to Zika-exposed mothers in the United States and U.S. territories had severe birth defects, including an abnormally small head and brain damage. But the large majority weren’t born with these defects.

A 2018 study of Zika-exposed babies from U.S. territories up to their first birthday, including some with abnormalities apparent at birth, reported a range of health problems possibly due to the virus (SN: 8/7/18).

The new study followed the 70 babies for a year and a half, assessing them at least once between the ages of 4 and 18 months old. The babies had normal fetal development and head circumference. But the results from the two neurodevelopmental tests — a questionnaire and an observational exam — suggest it’s possible that problems may not arise until later.

“We are still learning exactly how Zika exposure can affect a developing fetus and beyond,” says neurologist Nassim Zecavati of Georgetown University School of Medicine in Washington D.C., who was not involved in the research. More work is needed to determine the reasons for the delays in this group of children, and whether it’s a temporary decline, she says.

The neurodevelopmental differences found in the children can be addressed with physical and occupational therapy, Mulkey says. Her team will follow this group until they are 5 years old. “We don’t yet know the future of how these children are going to develop long-term,” she says.