**Question:** A patient presents with diarrhoea, analysis of stool on wet mount shows mobile protozoa without RBCs and pus cells. The diagnosis is -

A. Giardiasis
B. Entamoebiasis
C. Cryptosporidiosis
D. Cholera

**Correct Answer:** **C. Cryptosporidiosis**

**Core Concept:** Cryptosporidium is a protozoan parasite causing diarrheal illness. Cryptosporidiosis is a common cause of watery diarrhea, especially in immunocompromised patients. Cryptosporidium oocysts are typically seen in wet mounts of stool samples, and the absence of red blood cells (RBCs) and pus cells is a clue to this diagnosis.

**Why the Correct Answer is Right:** Cryptosporidiosis often presents with watery diarrhea, which does not show RBCs and pus cells on wet mount. Cryptosporidium is a protozoan parasite that infects the intestinal tract, causing inflammation and leading to watery diarrhea. Unlike other causes of diarrhea, Cryptosporidiosis lacks significant mucosal damage, which is why red blood cells and pus cells are absent in the wet mount.

**Why Each Wrong Option is Incorrect:**

A. Giardiasis: Giardia lamblia is another protozoan parasite causing diarrhea, but it often shows RBCs and pus cells in the wet mount due to significant mucosal damage.
B. Entamoebiasis: Entamoeba histolytica causes amebic dysentery, which presents with bloody diarrhea and shows RBCs and pus cells in the wet mount.
C. Cholera: Cholera is caused by Vibrio cholerae and presents with watery diarrhea, but typically shows RBCs and pus cells in the wet mount due to mucosal damage.
D. Cholera: Similar to option C, cholera shows RBCs and pus cells in the wet mount due to mucosal damage.

**Clinical Pearl:** In cases where diarrhea is suspected, examining the stool sample for the presence of RBCs and pus cells can help narrow down the differential diagnosis. However, a definitive diagnosis of protozoan infections (cryptosporidiosis, giardiasis, or amebiasis) may require additional tests like stool antigen detection or microscopic examination of formalin-fixed smears.