Virologists say they are deeply worried by the unprecedented Ebola epidemic in West Africa which has claimed more than 90 lives and may now also have struck north into the Sahel. A rare but extremely dangerous virus, Ebola is historically rooted in central Africa, although it has also caused past outbreaks in Uganda to the east. Except for a non-fatal case in Ivory Coast in 1994, when a lab researcher was infected while examining a dead chimp, Ebola had not previously been found in the west of the continent. How it got there is puzzling experts. The viral species now causing havoc is the Zaire strain of Ebola, which slays between 70 and 90 percent of those it infects and was last reported in the Democratic Republic of Congo in 2009. "When I heard about the outbreak, my initial suspicion was that it could be the Ivory Coast species," said Thomas Geisbert, an expert on haemorrhagic fevers at UTMB. "It turned out to be the Zaire species, which has never been connected with West Africa," Geisbert told AFP by email. "I am very concerned, because I think we still don't know how the virus got into this region or the size of the boundaries of the affected area." The Agence France-Presse article is getting widespread international coverage.