Sera positive for Australia antigen contain round or ovoid particles with an average diameter of 20 nm.1 Tubular forms of similar diameter1 and carrying transverse striations with a periodicity of 3 nm2 are usually present. Dane et al3 described a large round particle of 42 nm average diameter in addition to small particles and tubules. The former particles are present at a concentration at the limit of detection by the electron microscope. They may, therefore, be present in all sera positive for Australia antigen. The three types have a virus-like structure. It is not known, however, which type if any is responsible for the infection in Australia antigen-positive blood. Dane et al suggested that the infectious virions of serum hepatitis may be part of the large particles.
This study provides additional information on the nature of the large particle found in a chimpanzee with chronic antigenemia. Further