**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 a cell-mediated immune response, leading to tissue damage and impairment of the affected organs.

**Why the Correct Answer is Right**
The correct answer is related to the fact that leprosy primarily affects the peripheral nerves, skin, and mucous membranes. The disease is known to cause damage to the peripheral nerves, leading to sensory and motor deficits. However, certain organs are not directly affected by the disease. Leprosy does not typically affect the internal organs such as the heart, lungs, or liver, except in rare cases where the disease has progressed to the advanced stage.

**Why Each Wrong Option is Incorrect**
* **Option A:** Leprosy does affect the skin, causing lesions and discoloration. Therefore, this option is incorrect.
* **Option B:** Leprosy affects the peripheral nerves, leading to sensory and motor deficits. Therefore, this option is incorrect.
* **Option C:** Leprosy affects the mucous membranes, particularly in the eyes and nose. Therefore, this option is incorrect.

**Clinical Pearl / High-Yield Fact**
It is essential to note that leprosy can affect the eyes, leading to vision impairment or blindness. Therefore, patients with leprosy should undergo regular eye examinations to prevent complications.

**Correct Answer: D.**