A patient present with diarrhoea. Analysis of stool on wet mount shows mobile protozoa without RBCs and pus cells. The diagnosis is:
**Core Concept**
The patient's symptoms and stool analysis are indicative of a protozoal infection, specifically giardiasis, which is caused by the protozoan *Giardia lamblia*. This parasite infects the small intestine and can cause diarrhea, malabsorption, and weight loss.
**Why the Correct Answer is Right**
The presence of mobile protozoa without RBCs and pus cells in the stool is characteristic of giardiasis. *Giardia lamblia* trophozoites are flagellated and can be seen on a wet mount of the stool. The absence of RBCs and pus cells suggests that the infection is not accompanied by significant inflammation or bleeding. Giardiasis is often acquired through the ingestion of contaminated water or food.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely a distractor and not a valid answer choice.
**Option B:** This option might be a different protozoal infection, such as *Entamoeba histolytica*, which can cause dysentery with the presence of RBCs and pus cells in the stool.
**Option C:** This option might be a bacterial infection, such as *Salmonella*, which can cause diarrhea but would typically be accompanied by RBCs and pus cells in the stool.
**Clinical Pearl / High-Yield Fact**
It's essential to note that giardiasis can be asymptomatic in some individuals, and the diagnosis is often made based on the presence of the parasite in the stool. Treatment typically involves metronidazole or tinidazole.
**Correct Answer: C.**