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Children exposed to Zika in utero were more likely to develop microcephaly. Getty Images
  • Nearly one-third of children who were exposed to the Zika virus in utero exhibited developmental delays as toddlers.
  • The virus can affect brain tissue and leave calcium deposits that can affect an infant after they are born.
  • The CDC reports that there have been at least 20 cases of Zika diagnosed in U.S. states and territories this year.

Even when Zika virus doesn’t cause abnormalities to an infant’s head structure, it can still result in developmental delays. Almost one-third of children with Zika had developmental delays and other problems, according to a new study published this week in Nature Medicine.

Dr. Karin Nielsen-Saines, the lead author and a pediatric infectious disease specialist at the University of California, Los Angeles, said her team has followed the 216 children from the time their mothers were pregnant and were diagnosed with Zika.

A small number of children born with microcephaly did experience symptom improvement. Also, a small number of the children born without symptoms of microcephaly went on to develop the congenital condition. The researchers also found that children exposed to the virus had a higher rate of autism.

Nielsen-Saines said she has been surprised to find that how infants appear at birth does not necessarily predict how they will be in the years to come in terms of development, she told Healthline.

“Certainly the small number of children with severe birth defects will tend to do poorly, but some children with more subtle abnormal neurologic exams in infancy did better than expected in terms of development… others who seemed normal at birth had poor developmental scores in the second or third year of life,” she said.

Exposure to the virus does not necessarily mean infection, Nielsen-Saines noted. “Not all 216 exposed children in our cohort have a bad prognosis,” she said.

About one-third of children were below average in terms of development or had eye or hearing deficits. About two-thirds of them were normal in terms of neurodevelopment, she said.

“This is a condition we know very little about in terms of long-term follow-up. We know for sure there is a risk of developmental problems so we need to monitor these children over time to see if they don’t have any learning disabilities when they become school age, if they don’t have a higher chance of developing hearing problems or any other neurologic or neurodevelopmental condition,” she said.

Children who were exposed to Zika virus infection, even if they are doing well and don’t exhibit any developmental delays, need to continue to have close follow-up of their vision, hearing, and development, said Dr. Sarah B. Mulkey, a fetal-neonatal neurologist at Children’s National in Washington, D.C. who has studied children with Zika and their mothers.

“Early identification of a child with a developmental problem can enable special therapies or treatments to help improve the child’s development as much as possible,” Mulkey added.

Zika virus is neurotropic and infects brain cells, Nielsen-Saines explained. It can infect neuro progenitor cells and stops cells from developing, and it can induce calcium deposits in the brain and destroy brain tissue. It can also affect the optic nerve and retina, as well as hearing.

“So in its most severe forms Zika can induce findings consistent with cerebral palsy and in that sense it can be similar to children who have cerebral palsy for other reasons,” Nielsen-Saines said.

Researchers are not yet sure as to the mechanism that causes more common and subtle forms of mild to moderate developmental delays.

“The bottom line is that it’s not possible to predict how all Zika exposed children will fare in the future,”she added.

Nielsen-Saine plans to study the affected children in the future.

Micaela Martinez, PhD, an infectious disease ecologist at Columbia University’s Mailman School of Public Health, explained that there isn’t enough data to confirm what the long-term implications of Zika may be until the patients are studied in the future.

“We only know what’s happening two… three years later,” Martinez told Healthline. “There could be things that pop up in adolescence later in life. We’ll be discovering things decades later.”

The study was a small study that lacks a properly matched control group, said Nathan Grubaugh, PhD, whose lab at the Yale School of Public Health tracks viruses including Zika. For instance, Grubaugh would have liked to have seen data in the study on the normal rate of children from Rio de Janeiro who have developmental issues, especially children from poor families with a greater chance for exposure.

Instead of the numbers, he would like people to focus on the fact that exposure to Zika virus during pregnancy may cause long-term developmental problems with some children.

All periods of gestation can be sensitive for the effects of congenital viruses. They are not at risk only during early pregnancy; that’s just when they are most vulnerable, though, Martinez noted.

“Unfortunately Zika virus has found a way to overcome our innate barriers to interrupt development,” Grubaugh added. “This may be one of the greatest infectious disease challenges of our generation.”

Zika virus infection can have life-long consequences for the brain, added Alysson R. Muotri, PhD, a professor at the UC San Diego School of Medicine. He worked on a drug that blocks viral replication and vertical transmission but hasn’t been tested in pregnant women.

There is still travel guidance in place pertaining to Zika. The Centers for Disease Control and Prevention (CDC) recommends pregnant women discuss potential risks with their doctor if they are going to an area that has had a Zika outbreak in the past.

The CDC monitors potential cases worldwide. Certain countries, including the United States, had Zika outbreaks only in a few select areas, so it doesn’t mean the entire country is a risk to visit. Currently according to the CDC map there is no current outbreak of the virus.

But experts say the virus hasn’t disappeared for good.

“It hasn’t gone away. Zika cases are still rolling in,” Martinez said, noting that women in the continental United States are still contracting the virus.

The CDC reports that there have been at least 20 cases of Zika diagnosed in U.S. states and territories this year.

“People should still be vigilant to protect themselves from mosquitoes as the threat is not gone,” added Grubaugh.

“Now that Zika has largely dropped out of the media spotlight, it is easy to assume that there is no risk. However, it is likely that there will continue to be ongoing Zika transmission,” Dr. Denise J. Jamieson, a professor in the department of gynecology and obstetrics at Emory University School of Medicine, told Healthline. She led the CDC’s response to Zika in 2016 and 2017.

In positive news, there are clinical trials to better understand the virus and research into a potential vaccine. Some experts think it could be years away, though.