Most common cause of diarrhea in AIDS patients:
**Core Concept**
Cryptosporidiosis is an opportunistic infection caused by the protozoan parasite Cryptosporidium, which affects individuals with weakened immune systems, particularly those with AIDS. The parasite invades the epithelial cells of the small intestine, leading to malabsorption and diarrhea.
**Why the Correct Answer is Right**
The correct answer is Cryptosporidiosis because it is the most common cause of diarrhea in AIDS patients due to their compromised immune status. The parasite's invasion of the small intestine leads to the disruption of the brush border enzyme activity, particularly lactase, resulting in malabsorption of carbohydrates and subsequent diarrhea. Additionally, the inflammation caused by the parasite can lead to increased permeability of the intestinal mucosa, further contributing to the diarrhea.
**Why Each Wrong Option is Incorrect**
**Option A:** Giardiasis is another opportunistic infection that can cause diarrhea in AIDS patients, but it is not the most common cause. Giardiasis is caused by the protozoan parasite Giardia lamblia, which can lead to malabsorption and diarrhea through a different mechanism.
**Option B:** Cytomegalovirus (CMV) can cause gastrointestinal symptoms, including diarrhea, in AIDS patients, but it is not the most common cause. CMV infection can lead to inflammation and damage to the intestinal mucosa, resulting in symptoms like diarrhea.
**Option C:** Microsporidiosis is another opportunistic infection that can cause diarrhea in AIDS patients, but it is not the most common cause. Microsporidia are a group of intracellular parasites that can cause malabsorption and diarrhea through a different mechanism.
**Clinical Pearl / High-Yield Fact**
AIDS patients with diarrhea should be evaluated for opportunistic infections, and a stool examination for ova, parasites, and acid-fast bacilli should be performed to identify the underlying cause.
**Correct Answer: C. Cryptosporidiosis**