Serological marker of infectivity of Hepatitis is?
**Core Concept**
The question is testing the understanding of the serological markers associated with the different stages of Hepatitis B virus (HBV) infection. The correct answer will indicate the marker that is most closely associated with the infectivity of the virus.
**Why the Correct Answer is Right**
The infectivity of HBV is primarily determined by the presence of the hepatitis B e-antigen (HBeAg) in the serum. HBeAg is a protein that is secreted by infected hepatocytes and is a marker of viral replication and infectivity. When HBeAg is present, it indicates that the virus is actively replicating and the individual is highly infectious. The presence of HBeAg is also associated with a higher viral load and a greater risk of transmission.
**Why Each Wrong Option is Incorrect**
* **Option A:** HBsAg (Hepatitis B surface antigen) is a marker of infection, but it does not necessarily indicate infectivity. HBsAg can be present in both acute and chronic infections, and individuals with HBsAg can be in a variety of stages of infection, including latent and non-infectious.
* **Option B:** HBeAg-anti-HBe antibody complex is a marker of resolving infection, but it is not a marker of infectivity. The presence of this complex indicates that the individual is transitioning from an infectious to a non-infectious state.
* **Option D:** Anti-HBc (antibody to hepatitis B core antigen) is a marker of past or current infection, but it does not indicate infectivity. Anti-HBc can be present in both acute and chronic infections, and it does not differentiate between the two.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the presence of HBeAg is not the only factor that determines infectivity. The viral load and the presence of other markers, such as HBV DNA, can also play a role in determining the risk of transmission.
**Correct Answer: C. HBeAg**