Cryptosporidium Life Cycle
See
Apicomplexa Life Cycle
Oocysts* are ingested in contaminated food or water.
Within the intestine, excystation occurs: sporozoites* are released from the oocyst.
- The sporozoites attach to intestinal epithelial cells.
- Rather than invading the cells, the sporozoites cause the microvilli to fuse and expand, enveloping the parasite.
- Parasite enters the trophpozoite stage, feeds upon nutrition taken from the host.
Then, merogony, a type of asexual reproduction occurs, and produces 4-8 merozoites.* (type I merozoites)
- The merozoites enter the intestinal lumen, and infect new enterocytes.
- The merozoites replicate:
– Asexual reproduction (via merogony) produces more merozoites (some type I, some type II merozoites), which can, in turn invade new enterocytes.
– Sexual reproduction -
gametogony: type II merozoites produce macrogamonts and microgamonts, which go on to produce macrogametes and microgametes.* (we omit the gamont stage in our diagram, for simplicity).
The gametes fuse to form a zygote.*
The zygote goes through sporogony to ultimately produce the infective sporulated oocyst.*
– Be excreted in the feces to find a new host
– Invade intestinal epithelial cells of the current host, producing self-infection.
It is thought that the oocysts that remain in the host and cause self-infection are thinner walled than the oocysts that are excreted in the feces.
References:
Apicomplexa. Accessed November 8, 2018. https://www.tulane.edu/~wiser/protozoology/notes/api.html
Cryptosporidium life cycle. Accessed November 8, 2018. https://www.tulane.edu/~wiser/protozoology/notes/crypt_lc.html
Leitch, Gordon J, and Qing He. “Cryptosporidiosis-an Overview.” Journal of Biomedical Research 25, no. 1 (January 2011): 1–16. https://doi.org/10.1016/S1674-8301(11)60001-8.
Levinson, W. Review of Medical Microbiology & Immunology. 14th ed. McGraw-Hill Education, 2016.
