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 Manifestations
Incubation period of 1 week
Watery diarrhea with abdominal cramping, malaise, anorexia, and weight loss
Fever, if it occurs, is low-grade
One of the only intestinal protozoa that can cause a peripheral eosinophilia
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
