WASHINGTON (AP) – New details about the possible effects of the Zika virus on the fetal brain are emerging as researchers report finding an extremely abnormal brain in a fetus whose mother suffered Zika symptoms at the end of the first trimester while she was living in Brazil. The mosquito-borne virus has been linked to a birth defect called microcephaly, an abnormally small head. Wednesday’s study offers additional biologic clues.

The woman returned to Europe late in her pregnancy, when scans diagnosed microcephaly. In a post-abortion autopsy, European researchers found the fetal brain not only was a fraction of the proper size but also lacked the usual crinkly neural folds. They found the virus in the brain but not in other organs. The study was published by the New England Journal of Medicine.