**Core Concept**
Leprosy, caused by Mycobacterium leprae, is a chronic bacterial infection affecting the skin, peripheral nerves, and mucous membranes. It is characterized by cell-mediated immunity, with the disease severity depending on the host's immune response.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of leprosy. Leprosy primarily affects the peripheral nerves due to the bacteria's tropism for Schwann cells, leading to nerve damage and loss of sensation. The disease also affects the skin, causing hypopigmented or erythematous patches. In lepromatous leprosy, there is a high bacterial load and a poor immune response, leading to widespread tissue damage. In tuberculoid leprosy, there is a strong cell-mediated immune response, resulting in granulomatous inflammation and limited tissue damage.

**Why Each Wrong Option is Incorrect**
* **Option A:** Leprosy is primarily a disease of the skin, peripheral nerves, and mucous membranes, which is true.
* **Option B:** Leprosy is caused by Mycobacterium leprae, which is true.
* **Option C:** Leprosy is characterized by cell-mediated immunity, which is true.
* **Option D:** Leprosy primarily affects the liver, which is false. Leprosy primarily affects the skin, peripheral nerves, and mucous membranes.

**Clinical Pearl / High-Yield Fact**
Leprosy can be transmitted through close contact with an infected person, usually through respiratory droplets. It is essential to maintain proper hygiene and avoid close contact with individuals suspected of having leprosy.

**Correct Answer:** D. Leprosy primarily affects the skin, peripheral nerves, and mucous membranes, not the liver.