Antigenic analysis of strains of Ebola virus: identification of two Ebola virus serotypes.

A sensitive radioimmunoassay has been adapted for Ebola virus antigens and antibodies to them. It uses 125I-labeled staphylococcal protein A and a specially designed filter manifold. The assay is applicable to the sera of humans and to a wide range of animal sera. Virus isolates from two discrete outbreaks of Ebola hemorrhagic fever that occurred in 1976 were shown by this assay to be antigenically distinct. This lack of identity was further confirmed by cross-absorbing antisera to each isolate with antigens of the heterologous virus strain. The advantages of this assay include the use of noninfectious antigens, the requirement for only small quantities of serum, the capability of screening large numbers of sera, the speed of execution, and the objectivity of end point determination.