Cryptosporidium hominis

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

Background

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
  • Daycares (more common than Giardia)
  • Also seen with petting zoos and cider
  • Higher rates of transmission in MSM
• 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 Manifestations

• Incubation period 7 days (range 1 to 30 days)

Immunocompetent adults

• Associated with waterborne outbreaks, travel, animal contacts, or child contacts
• Watery (to mucoid) diarrhea and malabsorption, more lower bowel symptoms
• 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

Childhood diarrhea

• Causes about 10-15% of acute childhood diarrhea in developing countries
• Presents with watery diarrhea, cramps, and nausea and vomiting
• May also have fever, cough, dyspnea, and foul-smelling stool
• Can turn into chronic diarrhea and malabsorption

People living with HIV

• 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

Other immunocompromised patients

• May present similarly to HIV
• Includes solid organ transplant, hematopoietic stem cell transplant, and hyper-IgM syndrome

Diagnosis

• Stool microscopy
  • Seen on modified acid-fast staining (70% sensitive)
  • Can do immunofluorescence as well (more sensitive)
• Stool antigen
• PCR

Management

• For immunocompetent hosts, supportive care, including fluids and antimotility agents like loperamide, is generally adequate
• In immunocompetent hosts: nitazoxanide 500 mg p.o. twice daily for 3 days
  • Not approved in Canada, needs SAP
• In severely immunocompromised patients, may not be curable without reversing immunosuppression
  • Can treat with nitazoxanide 500 to 1000 mg p.o. twice daily for 14+ days
• Other medications
  • Paromomycin likely inferior to nitazoxanide
    • Dose is 500 mg p.o. three to four times daily for 14 days
  • Macrolides likely ineffective
  • Rifaximin and albendazole need more study

Further Reading

• Treatment of human intestinal cryptosporidiosis: A review of published clinical trials. Int J Parasitol. 2021;17:128-138: doi:10.1016/j.ijpddr.2021.09.001