Biologic Differences Between Strains of Ebola Virus from Zaire and Sudan

Abstract

Studies of three outbreaks of Ebola hemorrhagic fever in Zaire and Sudan have shown that human mortality resulting from Zaire strains of Ebola virus was 90% while that resulting from Sudan strains was 55%–65%. Zaire strains were much easier to isolate in cell culture than all of the Sudanese agents; also, fewer than 10 infectious particles of a Zaire strain were lethal for suckling mice, whereas 10,000 infectious particles of a Sudan strain failed to kill any of these animals. These biologic data indicate that these antigenically related viruses are different, a conclusion supported by genetic, biochemical, and immunologic data.