Viral families and hepatitis: Which hepatitis virus belongs to the family Hepadnaviridae?

Introduction / Context:
Knowing viral taxonomy links genome type to replication strategy and clinical behavior. Hepadnaviridae are partially double-stranded DNA viruses with reverse transcription in their life cycle.

Given Data / Assumptions:

• Hepatitis viruses A–E are unrelated families with different genomes.
• Hepadnaviridae hallmark: relaxed circular, partially double-stranded DNA and reverse transcriptase.
• Hepatitis D is a defective RNA agent requiring coinfection with HBV.

Concept / Approach:
HBV (Hepatitis B virus) is the prototypical Hepadnavirus. HAV is a picornavirus (nonenveloped, positive-sense RNA). HDV is a small circular RNA satellite (deltavirus) that depends on HBV surface antigen to assemble; it is not a member of Hepadnaviridae.

Step-by-Step Solution:
Identify which hepatitis virus has a DNA genome with reverse transcription.Select Hepatitis B virus as the sole correct member of Hepadnaviridae.Exclude HAV and HDV based on family and genome.

Verification / Alternative check:
HBsAg/HBcAg serology and antiviral targets (reverse transcriptase inhibitors) corroborate HBV’s hepadnaviral nature.

Why Other Options Are Wrong:
HAV and HDV are different families/agents; “All of these” is therefore incorrect.

Common Pitfalls:
Assuming all hepatitis viruses are related because of disease site; in reality, their taxonomy diverges widely.

Final Answer:
Hepatitis B virus