<prompt> Hepatitis D virus delta agent is a defective virus that can replicate only in cells already infected with which of the following viruses?Hepatitis A virusEpstein-Barr virusHepatitis G virusHepatitis B virus  <response>: Hepatitis D virus is a defective virus with an RNA genome and a hepatitis B surface antigen envelope. Two types of HDV infection occur: simultaneous HDV and HBV infection, or HDV superinfection with chronic HBV infection. Diagnosis is made by demonstrating IgM or IgG antibodies, or both. 