Health experts and scientists have suspected the link for many months now, but a recent report in the New England Journal of Medicine has definitively concluded Zika causes microcephaly. "It is now clear that the Zika virus causes microcephaly," said Tom Frieden, the director of the CDC.
Microcephaly is defined as abnormally small head and brain size in babies. And health officials noticed such cases correlated to increased Zika virus infections. They also found Zika virus in fetal tissues, and cell culture experiments show Zika has a propensity for nerve and brain cells. Analyzing all the evidence as a whole, the report stated: "... a causal relationship exists between prenatal Zika virus infection and microcephaly."
There is no smoking gun, however. Researchers are still unsure when Zika acts during pregnancy and the exact mechanisms behind its effects. And given its propensity for nerve tissues, scientists are investigating other possible brain defects in babies and in adults. But now that the cause is official, scientists are encouraged more than ever to discover vaccines or other ways to prevent the virus from causing more birth defects.