Cryptosporidium hominis

• A member of the Cryptosporidium species which causes diarrheal disease in humans
• Similar to Cryptosporidium parvum which typically infects cows, but can also infect humans

Microbiology

• Protozoan parasite in the genus Cryptosporidium

Epidemiology

• Infects humans, but can also infect cows, mice, gnotobiotic pigs, and rarely other species
• Transmitted fecal-oral via environmental contamination (such as recreational water), and can be spread person-to-person
  • Outbreaks are most commonly associated with drinking water, even when properly treated
• Resistant to chlorination and can survive in the environment up to 6 months
• In developing countries, primarily affects children less than 5 years
• In developed countries, primarily affects adults, related to travel
  • Causes 2-6% of traveller's diarrhea

Life Cycle

• Host ingests an oocyst (needing as few as 10 to cause disease)
• The oocyst excyst in the stomach and proximal small bowel, releasing four sporozoites
• Sporozoites bind to the intestinal epithelial cells and becomes vacuolized by the host cell membrane
• In the parasitophorous vacuole, they reproduce asexually into further sporozoites, which divide into type I meronts
• The type I meronts mature and release motile merozoites
• The merozoites again attach to the intestinal epithelial cells
• Merozoites then either reproduce asexually, as above, or sexually
  • Sexual reproduction involves a macrogamont and microgamont, which form a zygote
  • The zygote develops into an oocyst which contains four sporozoites
• Oocysts may be involved in auto-inoculation (if thin-walled) or environmental contamination (if thick-walled)

Pathophysiology

• Infection activates nuclear factor kappa B (NF-κB), which activates a large response
• Infection results in increased permeability of the intestinal mucosa
• T-cells are involved, with chronic infection in patients who are CD4-deplete

Clinical Presentation

• Incubation period 7 days (range 1 to 30 days)
• Watery diarrhea and malabsorption
• Chronic infection more common in HIV with CD4 <180 and X-linked hyper-IgM
• Associated with waterborne outbreaks of diarrhea