**Question:** Epidemiological marker of Hepatitis – B is

A. Viral hepatitis
B. Hepatitis B surface antigen (HBsAg)
C. Hepatitis B core antibody (anti-HBc)
D. Hepatitis B e antigen (HBeAg)

**Core Concept:** Hepatitis B virus (HBV) is a DNA virus that causes acute and chronic liver infections. The presence of certain viral markers helps in diagnosing and tracking the course of Hepatitis B infection.

**Why the Correct Answer is Right:** Hepatitis B is primarily diagnosed using the detection of viral markers in the patient's blood. Hepatitis B surface antigen (HBsAg) is the primary marker indicating an active HBV infection. It is present in the blood of patients during the acute phase of infection and also in those with chronic infection.

**Why Each Wrong Option is Incorrect:**

A. Viral hepatitis is a broad category, not specific to Hepatitis B.
B. Hepatitis B core antibody (anti-HBc) indicates past exposure to HBV, not an active infection.
C. Hepatitis B core antibody (anti-HBc) is usually detected during the convalescent phase after an acute infection, indicating past exposure, not current infection.
D. Hepatitis B e antigen (HBeAg) is present in the blood during the acute phase of infection and is a marker for active HBV replication. However, it is not as widely used as HBsAg for diagnosis.

**Clinical Pearl:** The detection of HBsAg is essential for diagnosing an active HBV infection, while other markers like HBV DNA, anti-HBs, and anti-HBc are used to understand the infection history and immune response. Regular monitoring of these markers is crucial in managing patients with chronic Hepatitis B infection.

**Correct Answer:** D. Hepatitis B e antigen (HBeAg)