Which hepatitis B marker appears first during acute infection and indicates ongoing viral replication?

Explanation

## Temporal Sequence of HBV Markers and Viral Replication **Key Point:** HBeAg (hepatitis B e antigen) is the marker that both appears early in acute HBV infection AND specifically indicates ongoing viral replication and high infectivity. ### Chronological Order of Appearance in Acute HBV Infection 1. **HBsAg** — the very first marker to appear (4–12 weeks post-exposure), indicating active infection 2. **HBeAg** — appears shortly after HBsAg, signifying active viral replication and high infectivity 3. **Anti-HBc IgM** — appears around the time of symptom onset; the best marker of *acute* infection timing, but does NOT indicate viral replication 4. **Anti-HBc IgG** — appears later, persists for life 5. **Anti-HBe** — appears as HBeAg clears (seroconversion = reduced replication) 6. **Anti-HBs** — last to appear; indicates recovery and immunity ### Why HBeAg is the Correct Answer The stem asks for the marker that **appears first during acute infection AND indicates ongoing viral replication**. HBeAg satisfies both criteria: - It appears early in the acute phase (shortly after HBsAg) - It is the direct correlate of active viral replication (reflects HBV DNA polymerase activity and high viremia) - Its persistence beyond 6 months predicts progression to chronic hepatitis ### Why the Other Options Are Incorrect | Marker | Appears Early? | Indicates Replication? | |---|---|---| | **HBsAg (A)** | Yes (earliest) | No — surface antigen only; present even in non-replicating states | | **Anti-HBc IgM (B)** | At symptom onset | No — indicates acute infection timing, NOT replication | | **HBeAg (C)** | Yes (early) | ✅ Yes — direct marker of active replication | | **Anti-HBs (D)** | No (last to appear) | No — indicates immunity/recovery | **High-Yield:** HBeAg positivity correlates with HBV DNA levels and is used to monitor antiviral therapy response. Loss of HBeAg with appearance of anti-HBe (seroconversion) marks a reduction in viral replication. **Clinical Pearl:** Anti-HBc IgM is the gold standard for diagnosing *acute* HBV infection (including the window period), but it does NOT indicate viral replication — that role belongs to HBeAg (and HBV DNA quantification). [cite: Harrison 21e Ch 298; Mandell, Douglas & Bennett's Principles of Infectious Diseases]