A patient presents with diarrhea. analysis of stool on wet mount shows mobile protozoa without RBCs and pus cells. The diagnosis is

Mobile protozoa with the absence of RBC's and pus cells in stools in a patient with diarrhoea suggests giardiasis. In balantidium coli and entamoeba histolytica infections, pus cells and RBC's will be present in stools. Trichomonas hominis is considered as non-pathogenic