In 1977, a gastroenterologist in Turin, Italy, named Mario Rizzetto, first detected delta agent in hepatocytes of patients with chronic hepatitis B infections. This previously unrecognized nuclear antigen resembled Hepatitis B core antigen (HBcAg) and was thought to be a Hepatitis B-specific antigen.


The following article by Rizzetto et al. (1980) was the first publication that confirmed delta antigen as transmissible, defective, and requiring co-infection with HBV for infection.