The recent emergence of Zaire ebolavirus in West Africa has come as a surprise in a region more commonly known for its endemic Lassa fever, another viral hemorrhagic fever caused by an Old World arenavirus. Yet the region has seen previous ebolavirus activity. In the mid-1990s, scientists discovered Côte d'Ivoire ebolavirus (now known as Taï Forest ebolavirus) as a cause of a single reported nonfatal case in a researcher who performed a necropsy on an infected chimpanzee.