A known HIV patient on anti - retroviral therapy presented with diarrhea of six months duration. Stoll microscopy was done in which 10-30 micrometer cysts were seen, Kinyoun stain was positive. What is the most likely diagnosis?

Explanation

The identification of the parasite is based on the size of oocyst since the size of oocyst is 20 to 30 Micron the most likely parasite is Isospora. If the size was 4-8 micron the parasite would have been Cryptosporidium parvum.