A 28 years old male presented with diarrhea for 6 months. On examination the causative agent was found to be acid fast with 12 micrometer diameter. What is the MOST likely causative agent?
Cyclospora oocysts take days or weeks to become infectious, and because of this, direct person to person transmission through fecal exposure is unlikely to occur. Cyclosporiasis has been linked to waterborne and foodborne infections. Altered mucosal architecture with shoening of intestinal villi due to diffuse edema and infiltration of inflammatory cells leads to diarrhea, anorexia, fatigue, and weight loss. The duration of symptoms among untreated, non immune persons is often prolonged but ultimately self-limited, with remitting-relapsing symptoms lasting up to several weeks or months. The incubation period for Cyclospora infections is about 1 week, similar to infections with Cryptosporidium. The diagnosis can be made by detection of spherical 8- to 10-m oocysts in the stool, although routine stool ova and parasite (O+P) examinations are not sufficient. Specific fecal examinations must be requested to detect the oocysts, which are variably acid-fast and are fluorescent when viewed with ultraviolet light microscopy. All the parasites mentioned in the question cause chronic diarrhea (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. Ref: Brooks G.F., Carroll K.C., Butel J.S., Morse S.A., Mietzneron T.A. (2010). Chapter 46. Medical Parasitology. In G.F. Brooks, K.C. Carroll, J.S. Butel, S.A. Morse, T.A. Mietzneron (Eds), Jawetz, Melnick, & Adelberg's Medical Microbiology, 25e.
Cryptosporidium
Isospora
Cyclospora
Giardia