Hepatitis D virus (HDV) requires which essential co-factor from the host hepatocyte for entry, making it unable to infect cells without prior or simultaneous HBV infection?

• A HBV core antigen for genome packaging
• B HBV e-antigen for RNA replication
• C HBV X protein for transcriptional activation
• D HBV surface antigen (HBsAg) as the obligate envelope protein for HDV ✓

Explanation

HDV is a defective satellite virus that encodes only its own genome (negative-sense circular RNA with ribozyme activity) and delta antigen, but requires HBsAg from HBV to form its envelope for assembly, budding, and cell-to-cell transmission. Without HBV co-infection, HDV cannot complete its replication cycle. This explains why eradicating HBV with nucleot(s)ide analogues or preventing HBV with vaccination also prevents HDV. Simultaneous HBV/HDV infection (coinfection) has lower chronicity risk than HDV superinfection on chronic HBV.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.