A 38-year-old man with a history of fever associated with abdominal pain of 3-week duration presents now with a sudden onset of abdominal pain and copious vomiting. Plain abdominal x-rays reveal air under a diaphragm. A CT scan shows mesenteric lymphadenopathy and splenomegaly is found. Laparotomy is performed and 3 feet of ileum resected. The luminal aspect of the resected bowel shows marked ulceration of Peyer’s patches. What is the most likely diagnosis?

**Core Concept**
The case described involves a patient with a history of fever and abdominal pain, followed by sudden onset of severe symptoms and radiographic evidence of bowel perforation. The key finding is the marked ulceration of Peyer's patches in the resected bowel. Peyer's patches are lymphoid follicles in the ileum that play a crucial role in the immune response, particularly against intestinal pathogens.

**Why the Correct Answer is Right**
The clinical presentation, CT scan findings, and histopathological features are all consistent with **Typhoid fever**, caused by Salmonella Typhi. The bacterium invades the intestinal mucosa, leading to inflammation of Peyer's patches, which can progress to ulceration and bowel perforation. The patient's symptoms, such as fever, abdominal pain, and vomiting, are typical of typhoid fever.

**Option A:** **Option A** is incorrect because Whipple's disease is a different entity characterized by malabsorption, weight loss, and diarrhea, with histopathological features of PAS-positive macrophages in the small bowel.

**Option B:** **Option B** is incorrect because Crohn's disease is a form of inflammatory bowel disease that can cause ulceration and perforation, but it typically affects the colon and does not involve Peyer's patches.

**Option C:** **Option C** is incorrect because Yersinia enterocolitica is a bacterium that can cause gastrointestinal illness, but it is not typically associated with the marked ulceration of Peyer's patches seen in this case.

**Option D:** **Option D** is incorrect because Tuberculosis can cause abdominal pain and bowel perforation, but it is not typically associated with the specific histopathological features described in this case.

**Clinical Pearl / High-Yield Fact**
The presence of Peyer's patch ulceration is a classic histopathological feature of typhoid fever. This finding should prompt a high index of suspicion for this diagnosis in patients with compatible clinical and radiographic findings.

**Correct Answer: C. Yersinia enterocolitica is incorrect, the correct answer is not listed.**

✓ Correct Answer: A. Typhoid enteritis