**Core Concept**
Typhoid ulcer is a complication of typhoid fever, a systemic infection caused by Salmonella Typhi. The ulcer is a result of the body's immune response to the infection, leading to mucosal inflammation and ulceration in the gastrointestinal tract.

**Why the Correct Answer is Right**
The typhoid ulcer is typically located in the ileum, the last part of the small intestine. The ulceration is caused by the invasion of the intestinal mucosa by Salmonella Typhi, leading to inflammation and necrosis of the mucosal lining. The ulcer is often accompanied by bleeding, which can lead to hematemesis (vomiting blood) or melena (black, tarry stools). The pathogenesis of the typhoid ulcer involves the activation of various inflammatory mediators, including cytokines and chemokines, which recruit immune cells to the site of infection, leading to tissue damage and ulceration.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the typhoid ulcer is not typically located in the stomach.
* **Option B:** This option is incorrect because the typhoid ulcer is not caused by a viral infection.
* **Option C:** This option is incorrect because the typhoid ulcer is not a result of a mechanical obstruction in the intestine.

**Clinical Pearl / High-Yield Fact**
Typhoid fever can be prevented by vaccination, and early treatment with antibiotics can reduce the risk of complications, including the development of typhoid ulcers.

**Correct Answer: D. Ileal ulceration due to Salmonella Typhi infection.**