**Core Concept**
Dermatophytosis, also known as ringworm, is a fungal infection of the skin caused by a specific group of fungi called dermatophytes. These fungi obtain their nutrients by breaking down keratin, a protein found in the skin, hair, and nails of warm-blooded animals.

**Why the Correct Answer is Right**
Dermatophytes have a unique ability to invade and digest keratin, which is a key component of the skin's outer layer, hair, and nails. This process is facilitated by enzymes such as keratinases, which break down keratin into smaller peptides and amino acids that can be absorbed by the fungus. Dermatophytes can infect various parts of the body, including the skin (tinea corporis), hair (tinea capitis), and nails (tinea unguium).

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as dermatophytosis is not caused by bacteria. While bacterial infections can also cause skin infections, dermatophytosis is specifically caused by fungal pathogens.
**Option B:** Incorrect, as protozoa are single-celled organisms that are not responsible for dermatophytosis. Protozoal infections can cause a range of diseases, but dermatophytosis is a fungal infection.
**Option C:** Incorrect, as dermatophytosis is not caused by viruses. Viral infections can cause a range of skin conditions, including warts and herpes simplex, but dermatophytosis is a fungal infection.

**Clinical Pearl / High-Yield Fact**
Dermatophytes can be transmitted through direct contact with an infected person or animal, as well as through contaminated objects such as combs, brushes, and towels. Good hygiene practices, such as washing hands regularly and keeping the skin clean and dry, can help prevent the spread of dermatophytosis.

**Correct Answer: C. Fungi. Dermatophytes.**