**Core Concept**
High infectivity in Hepatitis infection refers to the stage at which the virus is most transmissible from person to person, typically during the prodromal phase of the disease. This period is characterized by a high viral load and the presence of symptoms such as fatigue, nausea, and jaundice.

**Why the Correct Answer is Right**
The correct answer is Hepatitis B. Hepatitis B virus (HBV) is highly infectious during the prodromal phase, which typically lasts for 1-2 weeks after exposure. During this period, the virus replicates rapidly, producing large amounts of viral particles that can be transmitted through bodily fluids, including blood and saliva. The high viral load and presence of symptoms make HBV highly contagious, especially in healthcare settings.

**Why Each Wrong Option is Incorrect**
**Option A:** Hepatitis A is primarily spread through the fecal-oral route and is not as highly infectious as Hepatitis B. Although it can cause significant morbidity, its transmission dynamics are different from those of Hepatitis B.

**Option B:** Hepatitis C is also transmitted through bodily fluids, but its incubation period is longer, typically ranging from 14-180 days. As a result, the virus is not as highly infectious as Hepatitis B during the prodromal phase.

**Option C:** Hepatitis D is a satellite virus that requires the presence of Hepatitis B for replication and transmission. Its infectivity is therefore closely tied to that of Hepatitis B.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Hepatitis B is highly infectious during the prodromal phase, and healthcare workers should take precautions to prevent transmission, including wearing personal protective equipment and following strict infection control protocols.

**Correct Answer: C. Hepatitis B.**