A pregnant lady with AIDS complaint of diarrhoea. Stool examination showed acid fast positive stain cysts. She is infected with which of the following organism?

Infection with Isospora belli is known to cause diarrhea and its is diagnosed by the presence of large oocysts in stool detected by modified acid-fast staining. This infection is acquired by the consumption of oocysts. Patients usually presents with fever, abdominal pain, and watery nonbloody diarrhea. In AIDS patients or immunocompromised patients it causes profuse watery diarrhea. Trimethoprim-sulfamethoxazole is effective in the treatment of this condition. Ref: Weller P.F. (2012). Chapter 215. Protozoal Intestinal Infections and Trichomoniasis. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.