<s>[INST] context: Infection is acquired from pigs and other animal reservoirs or from human carriers. The infective form is the cyst, which is ingested in contaminated food or drink. Excystment takes place in the small intestine and the liberated trophozoites reach the large intestine where they feed and multiply as lumen commensals. Infection is very often confined to the lumen and is asymptomatic. Clinical disease results only when the trophozoites burrow into the intestinal mucosa, set up colonies and initiate inflammatory reaction. This leads to mucosal ulcers and submucosal abscesses resembling the lesions in amoebiasis. Clinically also, balantidiasis resembles amoebiasis, causing diarrhoea or frank dysentery with abdominal colic, tenesmus, nausea and vomiting. Occasionally there may occur intestinal perforation with peritonitis and rarely involvement of genital and urinary tracts. Diagnosis Diagnosis is established by demonstration of the parasite in faeces. While motile trophozoites occur in diarrhoeic faeces, cysts are found in formed stools. TEXTBOOK OF MEDICAL PARASITOLOGY,CKJ PANIKER,6TH EDITION,PAGE NO 111 [/INST] question: A patient presents with diarrhoea, analysis of stool on wet mount shows mobile protozoa without RBCs and pus cells. The diagnosis is - | options: A: Balantidium coli B: plasmodium C: Trichomonas hominis D: Entamoeba hystolytica | answer: A </s>