**Core Concept**
Leprosy, also known as Hansen's disease, is a chronic bacterial infection caused by *Mycobacterium leprae* that primarily affects the peripheral nerves, skin, and mucous membranes. The disease is characterized by its variable presentation, ranging from mild to severe, depending on the host's immune response.

**Why the Correct Answer is Right**
Leprosy is a classic example of a cell-mediated immune response. In individuals with a strong cell-mediated immunity, the bacteria are effectively contained, and the disease presents as a mild form, known as tuberculoid leprosy. This form is characterized by a limited number of skin lesions and nerve involvement, with a preserved nerve function. In contrast, individuals with a weakened cell-mediated immunity, such as those with a genetic predisposition or concurrent immunosuppression, are more likely to develop the severe, lepromatous form of leprosy, which is characterized by widespread skin lesions, nerve damage, and significant disfigurement.

**Why Each Wrong Option is Incorrect**
**Option A:** Leprosy is caused by a virus, not a bacterium. This is incorrect because leprosy is caused by the bacterium *Mycobacterium leprae*, which is a member of the Mycobacteriaceae family.

**Option B:** Leprosy is primarily spread through respiratory droplets. This is incorrect because leprosy is primarily spread through close contact with an infected individual, often through skin-to-skin contact or through respiratory droplets in crowded environments.

**Option C:** Leprosy is a self-limiting disease that resolves on its own. This is incorrect because leprosy is a chronic disease that requires long-term treatment to prevent complications and prevent the spread of the disease.

**Clinical Pearl / High-Yield Fact**
The Ridley-Jopling classification is a widely used system for categorizing leprosy into five clinical forms, ranging from tuberculoid to lepromatous. This classification system is essential for clinicians to determine the appropriate treatment and management strategy for patients with leprosy.

**Correct Answer: B. Leprosy is primarily spread through close contact with an infected individual, often through skin-to-skin contact or through respiratory droplets in crowded environments.**