Ebola--a growing threat?

arenavirus. Yet the region has seen previous ebolavirus activity (see map). 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. The episode initiated a major research investigation in and around the Taï Forest region — an effort that failed to identify the reservoir of this new Ebola species. Since that incident, West African countries have not reported any evidence of the presence of ebolavirus. Ebolaviruses belong to the family Filoviridae, a taxonomic group of enveloped, nonsegmented, negative-strand RNA viruses that includes the genera marburgvirus and cuevavirus, with a single species each, and ebolavirus, with five distinct species (see figure). All known African ebolaviruses can infect humans and cause similar symptoms, but they vary in terms of disease progression and virulence, with case fatality rates ranging from less than 40% for Bundibugyo ebolavirus to approximately 50% for Sudan ebolavirus to 70 to 90% for Zaire ebolavirus.2 The virulence of Taï Forest ebolavirus is difficult to assess because there has been only a single recorded case, and the only identified Asian species, Reston ebolavirus, seems to cause asymptomatic infection in humans. Humans infected with ebolaviruses commonly present initially with nonspecific symptoms such as fever, vomiting, and severe diarrhea, with visible hemorrhage occurring in less than half the cases,2 as in the current outbreak.1 Owing to poor infrastructure, biosafety concerns associated with processes of patient care and autopsy, and the essential focus on disease containment during outbreaks, there has been little empirical study to elucidate the pathogenesis or pathology of human ebolavirus infection. The closest surrogate disease models are cynomolgus and rhesus macaques, which show clinical signs of viral hemorrhagic fever when infected with most ebolaviruses. Zaire ebolavirus is uniformly lethal in these macaques, and experts have assumed that its Ebola — A Growing Threat?