A group of researchers say they’ve taken a critical step in proving the Zika virus is most likely the cause of a rising number of microcephaly cases in Brazil. An investigation conducted on lab cultures, led by Hengli Tang, a professor of biological science at Florida State University, has shown that the virus destroys certain brain cells, which leads to serious birth defects.  

To conduct the study, the team grew the Zika virus in mosquito cells and then infected certain human brain stem cells, called cortical neural progenitors, with the viral mosquito cells. Tang said it only took three days for the infection to spread to the whole culture dish. Shortly after that, Tang and his team—in collaboration with researchers at Johns Hopkins University and Emory University—found several changes to the stem cells that appear to be consistent with the pathological features of microcephaly.

“We found the cell’s growth was slowed down and we found some defects in cell cycle progression,” says Tang. Additionally, they found the virus replicates using this type of cell.