How Dangerous Is Zika For Babies? Scientists Try To Figure Out The Answer : Goats and Soda One big part of the puzzle: Why have there been so many microcephaly cases in the northeastern tip of Brazil?

How Dangerous Is Zika For Babies, Really?

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DAVID GREENE, HOST:

Earlier this year, you might remember the Zika virus was spreading through the Americas, and the situation looked dire. Brazil was reporting more than a thousand cases of microcephaly, a condition in which babies are born with extremely small heads. And the director of the World Health Organization, Dr. Margaret Chan, was predicting there would be many more cases as the mosquito-borne virus spread.

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MARGARET CHAN: If this pattern is confirmed beyond Latin America and the Caribbean, the world will face a severe public health crisis.

GREENE: Now, that never happened. Most other countries are reporting far fewer cases of microcephaly. But as NPR's Michaeleen Doucleff reports, scientists are just realizing there's a much more widespread issue with Zika.

MICHAELEEN DOUCLEFF, BYLINE: What's so frightening about the Zika virus is that a very common insect - a tiny mosquito - could deliver such severe birth defects.

THOMAS FRIEDEN: It's horrific. What's happening is that the Zika virus is invading the brain of the developing fetus. It's destroying the neural tissue.

DOUCLEFF: That's Dr. Thomas Frieden at the Centers for Disease Control and Prevention. He says the virus stops the brain's growth. This makes the baby's brain very small at birth, but it also disfigures the skull. During normal development, the brain pushes on the skull as the brain grows bigger. But if the brain stops growing, there's no pressure on the skull.

FRIEDEN: And the skull of the infant, the fetus, is collapsing around the destroyed brain.

DOUCLEFF: But it looks like the chances of this happening are much lower than previously thought. It looks like the risk is about 3 percent for pregnant women who are infected with Zika. Dr. Karin Nielsen is a pediatrician at UCLA. She's been studying babies with Zika in Brazil.

KARIN NIELSEN: Well, 3 percent is a small amount, you know, of microcephaly. Certainly it's not astronomical as what had been projected.

DOUCLEFF: She says, so far, only a region in northeast Brazil has reported a high number of microcephaly cases - a few thousand. It's not yet clear why. Everywhere else, the numbers are much lower. Columbia has reported about 70 cases, Guatemala 15, and Bolivia just nine. That's been a relief to public health officials worried about the scale of the epidemic. But Nielsen thinks that relief will be short-lived because another issue has cropped up with Zika.

NIELSEN: There's been tremendous focus in microcephaly, and I think it's wrong to focus on microcephaly because most studies have actually shown that microcephaly is not the most common problem with Zika.

DOUCLEFF: Instead, babies who look healthy at birth are showing up with problems later on. They have terrible neurological problems, seizures, brain hemorrhages.

NIELSEN: There's deafness, blindness.

DOUCLEFF: And problems with babies' joints. Nielsen and her team recently found that nearly 40 percent of babies born with Zika in Rio de Janeiro had one of these problems, even though they didn't have microcephaly. The study needs to be repeated in other cities, but if the findings stand, Nielsen says, Zika's impact on a generation could be far more sweeping than previously thought. Michaeleen Doucleff, NPR News.

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