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

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

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)

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

Associated with waterborne outbreaks, travel, animal contacts, or child contacts
Watery (to mucoid) diarrhea and malabsorption
May also have abdominal cramping, nausea or vomiting, and fever
Lasts 5 to 14 days, but up to 100
However, recurs in about 40% and can become an intermittent or chronic diarrhea similar to irritable bowel syndrome

Most cases are asymptomatic or mild and self-limited
Chronic infection more common in HIV with CD4 <150, lasting up to 6 months
May also involve extraintestinal cryptosporidiosis, such as biliary or respiratory disease