Whipple’s disease is caused by.
**Core Concept**
Whipple's disease is a rare, systemic bacterial infection characterized by malabsorption, weight loss, and diarrhea. It primarily affects the small intestine but can involve other organs such as the heart, brain, and joints. The disease is caused by a specific bacterium that invades the intestinal mucosa.
**Why the Correct Answer is Right**
Whipple's disease is caused by *Tropheryma whipplei*, a Gram-positive, rod-shaped bacterium. The bacteria invade the intestinal mucosa, leading to malabsorption and other systemic symptoms. The exact mechanism of invasion is not fully understood, but it is believed to involve the adherence of bacteria to the intestinal epithelial cells, followed by their internalization and replication within the cells.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the correct causative agent of Whipple's disease.
* **Option B:** This option is incorrect because it is not a recognized pathogen associated with Whipple's disease.
* **Option C:** This option is incorrect because it is a different type of bacterial infection that affects the lungs, not the gastrointestinal tract.
**Clinical Pearl / High-Yield Fact**
Whipple's disease should be considered in the differential diagnosis of patients with unexplained malabsorption, weight loss, and diarrhea, especially in those with a history of travel or exposure to contaminated water.
**Correct Answer:** A. Tropheryma whipplei.