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Risk of severe birth defects from Zika virus may be as high as 13 percent

New study is the first to measure risk rates

John Moore/Getty Images

The Zika virus may cause microcephaly in unborn children at a rate as high as 13 percent, a new study has found. The condition, which can result from a pregnant mother contracting Zika from an infected mosquito, leads to babies born with abnormally small heads and severe brain damage. Typical rates for microcephaly range from 0.02 to 0.12 percent of all US births. New research, conducted by analyzing data from Brazil and published today in The New England Journal of Medicine, shows a staggering jump in the risk rate if a mother is infected with Zika in the first trimester.

The range of risk spans from 1 percent to 13 percent, the study says, as researchers could not be certain about the overall rate of infection in the population studied and the accuracy of microcephaly diagnoses. There was "a negligible association in the second and third trimesters," the authors write. At the moment, the research is restricted to Brazil, and no other country with local Zika transmissions has exhibited the increase in microcephaly rates. However, as Zika continues to spread, the situation in Brazil may be replicated elsewhere.

As Zika continues to spread, the situation in Brazil may be replicated elsewhere

The virus entered that country last year and has since sprouted up in more than 40 countries. With the upcoming Rio Olympics slated to start in August, some experts fear the virus could spread faster than health officials can contain it. Mosquito season in the US is kicking into high gear across the country, while the Centers for Disease Control monitors 279 pregnant women infected with Zika. The virus poses a danger to adults as well, as Zika has been linked to Guillain-Barré syndrome, a neurological auto-immune disease that can cause paralysis and death. The first reported Zika death in the US occurred last month in Puerto Rico.