Ans. is 'c' i.e., Cyclospora All the parasites mentioned in the question cause chronic diarrhoea {mostly in immunocompromised patients).All of them reveal oocyst on stool examination. In Giardiasis, parasite is also seen along with oocyst stool examination.Oocyst of all the organisms except giardia are acid fast. The diagnosis rests on the size of the oocyst.DIAGNOSIS OF INTESTINAL PROTOZOAL INFECTIONParasiteStoolFecal acid fast stainSize of the oocystGiardiaOocyst + Parasite 4 nuclei 8-12 x 7 x 10 pmCryptospo- ridiumOocyst+Small, 4-5 pm in diameterIsosporaOocyst+Large 25 pm in diameterCyclosporaOocyst+Medium 8-10 pm diameterMicrosporidiaSpores Special fecal stains, tissue biopsiesMore on this topicParasites causing chronic diarrhoeaGiardiaCryptosporidiosisIsosporaCyclosporaHookwormAmoebiasisStrongyloidesAcid fast organisms are -MycobacteriumLepra bacilliNocardiaIsosporaBacterial sporesRhodococcusSmegma bacilliSpermatic headCryptosporidiumCyclospora