New studies released Friday offer the strongest indication yet that the Zika virus is responsible for the dramatic increase in microcephaly in Brazil while simultaneously warning that condition could be just the tip of the iceberg for infected babies. Researchers working at three US colleges determined Zika specifically targets cells that will develop into brain cells, according to their study. Using stem cells, they found Zika infected up to 90% of neural progenitor cells, killing one-third of them, in a process that would have "devastating results" to a developing brain, the BBC reports. Neural progenitor cells go on to form the brain's cortex—the exact same part of the brain that is shrunken in microcephaly cases.
While the new study doesn't prove Zika causes microcephaly, it strengthens that theory by showing that the virus can severely damage the brain, the Washington Post reports. "We're literally the first people in the world to know this, to know that this virus can infect these very important cells and interfere with their function," says the study's lead author. Meanwhile, another study out of Brazil shows Zika may be connected to even more "grave outcomes" for babies than previously known, according to the AP. "It's much more than microcephaly," one doctor says. Ultrasounds on dozens of Zika-infected women showed abnormalities in 29% of their fetuses. Those abnormalities included growth issues, problems with the placenta, and even death.