Cryptosporidium parvum is an obligate intracellular parasite and has a
monoxenous life cycle. The infective stage is a resistant oocyst, about
3.5-5 µm in diameter, which can remain viable in water at 4C for over 6
months.  Following ingestion and passage into the small intestine the oocyst
ruptures to release 4 sporozoites. which immediately penetrate the apical
epithelial cells or enterocytes of the intestinal villi. Once inside they
undergo multiple fission, merogony (schizogony), to produce 8 Type I
merozoites. The meronts eventually rupture releasing merozoites which
reinfect other enterocytes. These type I meronts can cycle in the host
indefinitely. After a number of generations, a second type of meront, type
II, are formed. The trigger for this is not known. The type II meronts only
have 4 merozoites. 
These merozoites appear to form the gametes, upon penetrating into the
enterocytes again. Some of the merozoites form a single female 
macrogametocyte and others divide to form 16 motile, but non-flagellated,
male microgametocytes. The microgametocytes rupture from the host cell and 
locate and fuse with a macrogametocyte to form a zygote. This is the only
diploid stage of the life cycle. Meiosis then follows, giving rise to 4 
haploid sporozoites within the oocyst.. The oocyst breaks out of the cell
and is passed out in the host feces. The prepatent period is generally about
4 
days with patency lasting 6-10 days. The reproductive cycle can be very
rapid, between 12-24 hrs leading to a rapid increase in the population
In normal immunocompetent hosts, the infection is acute and self limiting.
Surface proteins and glycoproteins are highly immunogenic and therefore
leads to rapid elimination of the parasite.  In immunocompromised hosts the
infection it is chronic and the numbers of parasites can soar resulting in
the invasion of secondary sites such as the duodenum, large intestine,
stomach, biliary and pancreatic ducts and respiratory tract and if untreated
can result in death.
The presence of the sporozoites results in changes in the host villi
including, blunting of villi, crypt hyperplasia, cellular infiltration of
the lamina propriaand the release of pro-inflammatory cytokines - IL6, IL8,
and/or TNF-a and an increase in cellular permeability.

Detection methods consist of finding oocysts in the stool or tissue with an
H&E or occasionally after formalin fixation with a modified Ziehl-Neelsen
method. I have had the best results with a Giemsa, PTAH and the
Auramine-rhodamine fluorescent technique.

Eric C. Kellar



	----------
	From:  marilyn.johnson@agric.gov.ab.ca
[SMTP:marilyn.johnson@agric.gov.ab.ca]
	Sent:  Tuesday, July 20, 1999 2:07 PM
	To:  histonet@Pathology.swmed.edu
	Subject:  Cryptosporidia

	Does anyone have a special stain to demonstrate cryptosporidia ?
	I have tried PAS, Grocott and Kinyoun's Acid Fast. The Parasitology
Lab. got
	very good results on smears but it's difficult to stain them after
routine
	processing.
	Any suggestions would be greatly appreciated !!
	Thanks.

	Marilyn Johnson
	Animal Health Labs.
	Edmonton, Alberta, Canada.