**Core Concept**
Syncytium formation is a characteristic feature of certain viral infections, where infected cells fuse together to form a multinucleated giant cell, also known as a syncytium. This process is mediated by viral proteins that induce cell-to-cell fusion.

**Why the Correct Answer is Right**
The measles virus is a paramyxovirus that causes measles infection. During the replication cycle, measles virus encodes for the fusion (F) protein, which plays a crucial role in the formation of syncytia. The F protein facilitates cell-to-cell fusion by interacting with the hemagglutinin (H) protein, resulting in the fusion of infected cells and the formation of multinucleated giant cells. This process is a hallmark of measles virus infection and contributes to the pathogenesis of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Herpes virus does not typically induce syncytium formation. While some herpesviruses can cause cell fusion, it is not a characteristic feature of herpesvirus infections.

**Option B:** Adenovirus can cause cell lysis and necrosis, but it does not typically induce syncytium formation. Adenovirus infections are often characterized by cell death and inflammation, rather than cell fusion.

**Option D:** Rabies virus is a lyssavirus that causes rabies infection. While rabies virus can cause neuronal degeneration and cell death, it does not typically induce syncytium formation.

**Clinical Pearl / High-Yield Fact**
Measles virus-induced syncytium formation is a key feature of measles infection and can be observed in infected tissues, such as the respiratory tract and lymphoid organs. This process contributes to the pathogenesis of measles and can be used as a diagnostic marker for the disease.

**✓ Correct Answer: C. Measles virus**