Serological marker of infectivity of Hepatitis ‘B’ is –
**Core Concept**
The serological markers of Hepatitis B infection are essential for assessing the patient's infectivity and disease progression. Hepatitis B virus (HBV) infection is characterized by the presence of various surface antigens (HBsAg) and antibodies, which serve as markers for different stages of the infection.
**Why the Correct Answer is Right**
The correct answer is the serological marker that indicates active viral replication and infectivity. HBV surface antigen (HBsAg) is a marker of active infection and is responsible for the transmission of the virus to others. It is present in the blood and other bodily fluids of infected individuals, making them contagious. HBsAg is a protein on the surface of the HBV virus, and its presence in the blood indicates that the virus is actively replicating and the individual is infectious.
**Why Each Wrong Option is Incorrect**
* **Option A:** HBeAg (Hepatitis B e-antigen) is a marker of viral replication, but it is not the primary serological marker of infectivity. Although HBeAg is associated with high viral replication and infectivity, its presence is not as sensitive or specific as HBsAg for indicating active infection.
* **Option B:** Anti-HBs (antibody to HBsAg) is a marker of immunity to HBV, either through vaccination or past infection. It does not indicate active infection or infectivity.
* **Option C:** Anti-HBc (antibody to HBcAg) is a marker of past or present infection, but it does not specifically indicate infectivity. This antibody is present in both acute and chronic infections, but it does not correlate with the level of viral replication.
**Clinical Pearl / High-Yield Fact**
Hepatitis B surface antigen (HBsAg) is a critical marker for assessing the infectivity of patients with HBV infection. It is essential to note that HBsAg can remain positive for many years in individuals with chronic HBV infection, making them long-term carriers of the virus.
**Correct Answer: C. Anti-HBc (antibody to HBcAg)**