Morphological and physical characteristics of an antigen associated with viral hepatitis type A (Botevgrad antigen).

Immune electron microscopy (IEM) was employed in studying faecal samples of viral hepatitis type A patients and their contacts, in whom the presence of an antigen, differing from the HBsAg, designated as Botevgrad antigen (BA) was proved by the CFT. Particles 25--28 nm in diameter, aggregated by sera positive for the anti-HAAg were established in the faecal samples. The buoyant density of these particles in CsCl was found to be 1.40 g/ml. Particles of the same buoyant density were established also in sera positive for BA which were aggregated in large masses with antiserum against BA obtained from rabbits. The associations between BA and HAAg are discussed.