NBC News – There’s no longer any doubt that the Zika virus causes birth defects, federal health officials said Wednesday.

The evidence has been piling up and there really had not been any doubt that Zika was causing horrific brain damage to unborn babies. But the Centers for Disease Control and Prevention made it official Wednesday in a publication rushed into the New England Journal of Medicine.

“It is now clear … that Zika does cause microcephaly,” CDC Director Dr. Tom Frieden told reporters in a briefing. “We believe the microcephaly is likely to be part of a range of birth defects.”

Zika’s been spreading in Brazil and since last year officials there noted a startling increase in the number of cases of microcephaly, a birth defect caused by an underdeveloped brain and marked by a notable small head.

There were doubts at first that Zika, once thought to be a pretty harmless virus, could actually be causing birth defects. Until Brazil started raising the alarm, doctors didn’t think it even made most people sick. Mosquito-borne viruses had never before been known to cause birth defects, although other viruses, such as rubella, are notorious for causing them.

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