<prompt> 24-year-old AIDS patient develops chronic abdominal pain, low grade fever, diarrhoea, malabsorption. Oocysts demonstrated in stool. Likely cause of his diarrhoea is:E. histolyticaG. lambliaMicrosporidiaIsospora belli  <response>: Ans is d i.e., Isospora belliRef: Harrison, 18the, p. 1731, 1732; 17the, p. 1313 Cryptosporidia, microsporidia and Isospora belli are the most common opportunistic protozoa that infect the GI tract and cause diarrhea in HIV-infected patients.HIV Infected PatientCryptosporidia 6-8 micronMicrosporidia 8-10 micronIsospora belli 23-36 micron Acid fast oocyst in stool Presence of organism in stoolAcid fast oocyst in stool No oocyst 