**Core Concept**
Mikulicz and Russell bodies are characteristic histopathological features of a specific infectious disease affecting the upper respiratory tract, particularly the nasal passages and paranasal sinuses. These inclusions are found in the cytoplasm of infected cells, such as macrophages and epithelial cells.

**Why the Correct Answer is Right**
Rhinoscleroma, caused by the bacterium *Klebsiella rhinoscleromatis*, is a chronic granulomatous disease of the nasal mucosa. The presence of Mikulicz and Russell bodies is a hallmark of this condition, resulting from the aggregation of the bacterial capsular polysaccharide and the host cell's cellular components. These inclusions are formed as a response to the bacterial infection, leading to the formation of granulomas and fibrosis in the affected tissues.

**Why Each Wrong Option is Incorrect**
**Option B:** Rhinosporidiosis is a distinct fungal infection characterized by the presence of rhinosporidium seeberi, which forms sporangia in the affected tissues. While it also affects the nasal mucosa, Mikulicz and Russell bodies are not associated with this condition.
**Option C:** Plasma cell disorders, such as multiple myeloma, are characterized by an abnormal proliferation of plasma cells, which can lead to the production of excessive amounts of immunoglobulins. However, Mikulicz and Russell bodies are not typically associated with these conditions.
**Option D:** Lethal midline granuloma is a term used to describe a group of conditions, including natural killer/T-cell lymphoma, which can affect the nasal passages and sinuses. While these conditions can also cause granulomatous inflammation, Mikulicz and Russell bodies are not characteristic of these diseases.

**Clinical Pearl / High-Yield Fact**
Mikulicz and Russell bodies are often seen in the context of chronic infections, particularly those caused by gram-negative bacteria. Recognizing these inclusions can help differentiate rhinoscleroma from other conditions that affect the upper respiratory tract.

**✓ Correct Answer: A. Rhinoscleroma**