NEET-PG 2020 — Microbiology

Q: A 35-year-old heterosexual patient diagnosed with HIV presents with watery diarrhea. The colonoscopic biopsy is shown below. Which of the following is your most probable diagnosis?

Cryptosporidium. ***Cryptosporidium*** - The image shows numerous small, round **Cryptosporidium oocysts** lining the **brush border** of the intestinal epithelial cells, a classic histological finding in disseminated disease in immunocompromised patients. - In an HIV patient with watery diarrhea, **Cryptosporidiosis** is a common opportunistic infection, especially when CD4 counts are low. *Giardia* - **Giardia lamblia** typically appears as teardrop-shaped trophozoites or oval cysts. Trophozoites would be motile in stool samples or adhere to the brush border but are much larger and morphologically distinct from the structures seen here. - While it causes watery diarrhea, the histological appearance does not match the small, bead-like structures on the epithelial surface. *CMV* - **Cytomegalovirus (CMV)** infection in the gut would typically show **cytomegalic cells** with characteristic **intranuclear inclusions** (owl's eye inclusions) and sometimes intracytoplasmic inclusions within various cell types, including endothelial cells and fibroblasts. - The image does not display these large, virally infected cells or inclusion bodies; instead, it shows numerous small parasitic forms on the surface. *Microsporidia* - **Microsporidia** are intracellular parasites that infect enterocytes and cause watery diarrhea in HIV patients. They are extremely small and often require special stains (e.g., modified trichrome, Warthin-Starry silver stain) or electron microscopy for definitive identification. - While they are small, the parasites in the image appear more superficial and exhibit a distinct spherical shape consistent with *Cryptosporidium* oocysts rather than the typically intracellular, punctate forms of microsporidia, which are harder to see with routine H&E staining without significant intracellular disruption.

21 Questions — Page 3 of 3

Q21

A 35-year-old heterosexual patient diagnosed with HIV presents with watery diarrhea. The colonoscopic biopsy is shown below. Which of the following is your most probable diagnosis?