Antigenic relationships among strains of African swine fever virus

Cross-reaction in hemadsorption inhibition tests with African swine fever viruses and swine immune sera permitted the separation of two antigenic subgroups, A and B. However, there are African swine fever viruses which cannot be included in these subgroups, thus constituting at least one third subgroup. Non-hemadsorbing African swine fever viruses are described which were isolated from pigs dying with chronical lesions of pneumonia as shown by autopsy; several hypotheses to explain the appearance of these nonhemadsorbing strains are advanced. Electron microscopy studies suggest that the subgroup-specific antigen is associated with the outer structural component of the virion, which derives from the cytoplasmic membrane of the infected cell.