Breakthrough study shows strong link between Zika Virus, severe birth defects

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There is still no direct confirmation Zika virus, spread by infected mosquitoes, is to blame more than 5,600 Brazilian babies born with abnormally small heads. But the CDC and other health organizations say the evidence of a link between Zika and microcephaly is growing.

The Atlanta-based agency is warning pregnant women to avoid more than 30 areas where the Zika virus is actively spreading.

Now a chilling new study, conducted by both American and Brazilian researchers, is driving home that warning.

The team followed 88 woman at a clinic in Rio de Janeiro. The researchers found when a pregnant women is infected and becomes symptomatic, there is a good chance the virus could do serious damage to her unborn baby.

The study found 29 percent of pregnant women given ultrasounds after testing positive for Zika virus had fetuses that suffered "grave outcomes," including fetal death and nerve damage that can lead to blindness.

And the virus may pose a threat not just in the first trimester, but throughout a woman's pregnancy.

Two women in the Brazil study, infected at 25 and 32 weeks gestation, lost their pregnancies, even though their previous ultrasounds prior to their infections were normal.

The study was published in the online version of The New England Journal of Medicine.

In another research study, published in the journal Cell Stem Cell, researchers say they may have a better understanding of how the virus may damage the developing brain.

They found Zika virus may directly target fetal brain cells, disrupting normal brain development.

Working quickly, they say, the virus infects the cells and causes them to die off. Then, it uses those damaged brain cells to reproduce itself and infect more cells.