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[Last Modified: ] |
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[Cryptosporidium
spp.] |
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Life cycle of Cryptosporidium
parvum and C. hominis.
Cryptosporidium
stages were reproduced from Juranek DD.
Cryptosporidiosis. In: Strickland GT, editor. Hunter’s Tropical Medicine and
Emerging Infectious Diseases, 8th ed. Philadelphia: WB Saunders; 2000.
Originally adapted from the life cycle that appears in Current WL, Garcia
LS. Cryptosporidiosis. Clinc Microbiol Rev 1991;4:325-58.
Sporulated oocysts, containing
4 sporozoites, are excreted by the infected host through feces and possibly other routes
such as respiratory secretions
.
Transmission of Cryptosporidium parvum and C. hominis occurs mainly through contact with
contaminated water (e.g., drinking or recreational water).
Occasionally food sources, such as chicken salad, may serve as vehicles for
transmission. Many outbreaks in the United States have occurred in
waterparks, community swimming pools, and day care centers. Zoonotic
and anthroponotic transmission of C. parvum and anthroponotic transmission of C.
hominis occur through exposure to infected animals or exposure to water contaminated by feces of infected animals
.
Following ingestion (and possibly inhalation) by a suitable host
, excystation
occurs. The sporozoites are released and parasitize
epithelial cells (,
)
of the gastrointestinal tract or other tissues such as the respiratory tract. In these cells, the parasites undergo asexual multiplication
(schizogony or merogony) (,
,
)
and then sexual multiplication (gametogony) producing microgamonts (male)
and macrogamonts (female)
. Upon fertilization of the macrogamonts by the microgametes
(),
oocysts (,
)
develop that sporulate in the infected host. Two different types of
oocysts are produced, the thick-walled, which is commonly excreted from the host
,
and the thin-walled oocyst
,
which is primarily involved in autoinfection. Oocysts are infective
upon excretion, thus permitting direct and immediate fecal-oral
transmission. Note that oocysts of Cyclospora cayetanensis, another important
coccidian parasite, are unsporulated at the time of excretion and do not become infective
until sporulation is completed. Refer to the life cycle of Cyclospora
cayentanensis for further details.
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