Cystoisospora belli

Background

Epidemiology

• Worldwide, but more in tropical and subtropical areas
• Can have outbreaks with daycare, animal exposures
• Mostly associated with HIV infection, but can also cause a traveller's diarrhea

Life Cycle

• Oocysts are shed into the environment
  • Each contains one sporoblast
  • Remain viable for months
• Oocysts sporulate in the environment before becoming infectious
  • Sporoblasts dividing and maturing into two sporocysts, which in turn divide and mature into two sporozoites each
• The sporulated oocyst (containing four sporozoites) is ingested
• In the proximal small bowel, the sporozoites are released and develop into merozoites
• The merozoites go through asexual reproduction, eventually followed by sexual reproduction that results in development of an immature oocyst, which is shed

Clinical Presentation

• Incubation period of 1 week
• Watery diarrhea with abdominal cramping, malaise, anorexia, and weight loss
• Fever, if it occurs, is low-grade
• Lasts 2 to 3 weeks, but can continue to shed oocysts for weeks after

Immunocompromised patients

• Includes HIV (CD4 <200) and chemotherapy
• Disease course may be more severe and may be chronic
• Can include hemorrhagic colitis

Management

• In HIV patients:
  • Trimethoprim-sulfamethoxazole DS po qid for 10 days
  • Alternative: ciprofloxacin 500 mg po bid for 7 days then three time weekly, pyrimethamine 75 mg po daily with folinic acid, or nitazoxanide