Hepatitis B Virus
The hepatitis B virus is a small DNA virus that belongs to the Hepadnaviridae family of viruses. The hepatitis B virus causes hepatitis B in humans. Related viruses in this family cause hepatitis in ducks, ground squirrels and woodchucks.
The hepatitis B virus contains an inner core and outer envelope. There is an outer shell (or envelope) composed of protein that is termed "surface antigen" or "HBsAg".
The surface antigen is generally produced in vast amounts, and the hepatitis B blood tests can detect this portion of the virus in the blood of infected individuals.
The outer shell surrounds an inner protein shell that is referred to as the core particle or "HBcAg", which contains the viral DNA and enzymes used in viral replication (called "DNA polymerase").