NEW YORK — A lab study has found that Zika can infect embryonic cells that help form the brain, adding to evidence that the virus causes a serious birth defect.

The mosquito-borne virus is spreading in Latin America and the Caribbean. Scientists are alarmed by indications that when it infects a pregnant woman, her baby may be born with a small head and a brain that hasn’t developed properly.

Previous studies have found Zika virus in the brains of babies with the defect who had died. Now the new study finds that in laboratory dishes, Zika can harm specific cells that help the brain develop. But experts caution that this doesn’t prove the virus causes the birth defect.

The research was published Friday by the journal Cell Stem Cell.