C. parvum and C. hominis LIFE CYCLE
Crypto begins its life cycle as sporulated oocysts (1) which enter
the environment through the feces of the infected host. There is some evidence that it can also be
spread by respiratory secretions.
The infective
oocysts reside in food and water (2).
Most transmission occurs through recreational water use, such as in
pools and lakes. Crypto has also entered
drinking water supplies, causing major outbreaks in cities around the
world. Oocysts are resistant to chlorine
treatment, presenting a major water purification problem during outbreaks. They can also withstand freezing
temperatures.
Infection occurs
when the oocysts are ingested by a suitable host (3). While in the intestines, the oocyst releases sporozoites which invade
the epithelial linings of the intestines or the lungs (depending on the method of
transmission). Within these cells, the
sporozoites undergo schizogony, or asexual reproduction. The sporozoites then enter a sexual
reproductive stage. Female macrogamonts
and male microgamonts develop, and fertilization occurs. The resulting zygote can develop into: a) a thick-walled oocyst that will exit the
host, or b) a thin-walled oocyst which will autoinfect the host.
The infectious
oocysts are passed through the feces (1).
These oocysts enter the environment to await ingestion by the next host.
From
Laboratory Identification of Parasites of Public Health Concern, CDC.
(http://www.dpd.cdc.gov/dpdx/HTML/Cryptosporidiosis.htm).