Question
Cryptosporidium
Answer
Cryptosporidium (species parvum/hominis) is a coccidian protozoan parasite, an important cause of watery diarrhoea, particularly significant as an opportunistic pathogen in AIDS patients, in whom it can cause severe, chronic, life-threatening diarrhoea.
Transmission: faecal-oral route via ingestion of the environmentally resistant oocyst in contaminated water (resistant to standard chlorination) or food.
Pathogenesis: ingested oocysts release sporozoites that invade the intestinal epithelium, developing within an intracellular but extracytoplasmic parasitophorous vacuole; resulting mucosal damage impairs absorption; disease severity depends heavily on host immune status — self-limiting in immunocompetent hosts, but chronic/severe in advanced AIDS (typically at CD4 counts below 100 cells/μL).
Laboratory diagnosis: modified Ziehl-Neelsen (modified acid-fast) staining of stool — small, round, acid-fast oocysts (4–6 μm); stool antigen ELISA and PCR are also available.
Treatment: supportive (rehydration) in immunocompetent hosts; nitazoxanide has some efficacy; in AIDS patients, restoration of immune function via antiretroviral therapy is the most effective approach.