**Core Concept**
Acute Hepatitis B is characterized by the presence of viral replication, inflammation, and liver damage. The presence of specific markers can indicate the stage of infection and aid in diagnosis. HBeAg is one such marker that is associated with viral replication and high infectivity.

**Why the Correct Answer is Right**
HBeAg is a protein produced by the hepatitis B virus during replication. Its presence indicates active viral replication, high levels of HBV DNA, and a high risk of transmission to others. HBeAg is often used as a marker to assess the infectivity of an individual with hepatitis B. The presence of HBeAg usually correlates with the presence of HBV DNA in the blood, making it a useful marker for monitoring the progression of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** HBsAg is a marker of hepatitis B infection, but it can persist even in individuals with chronic infection, not just acute infection.
**Option C:** Anti-HBc (IgM) is a marker of acute hepatitis B infection, but it is not as sensitive as HBeAg for detecting viral replication.
**Option D:** Anti-HBs is an antibody produced in response to vaccination or past infection and indicates immunity to hepatitis B, not acute infection.

**Clinical Pearl / High-Yield Fact**
During acute hepatitis B infection, individuals are highly infectious and can transmit the virus to others through bodily fluids. The presence of HBeAg indicates a higher risk of transmission, and public health measures should be taken to prevent further spread.

**✓ Correct Answer: B. HBeAg**