Practical Parasitology

Cryptosporidium parvum

• Size: 4 - 5 microns
• A protozoan measuring 4 - 5 microns with 4 sporozoites.
• C. parvum is an intracellular pathogen of the small intestine in animals and man.
• Infection results from the ingestion of oocysts, frequently the result of water and food contamination.
• One study showed that C. parvum is not limited to fresh water. Sewage and water runoff has contaminated shell fish in some areas. The eating of raw shellfish should be avoided to prevent cryptosporidiosis and the infection by other pathogens such as Salmonella typhi, Vibrio vulnificus and Campylobacter jejuni.(29) The same study showed that C. parvum oocysts survived salinity for a short period of time varying with salt concentration.
• Studies show that there may be two types of C. parvum. One that infects just humans and another that infects humans and animals (27). This may imply two different modes of transmission.
• Cryptosporidiosis is particularly serious for the AIDs patient. An infection, which for the immunocompetent patient is self limiting is manifested by severe chronic diarrhea for the immunocompromised.(28)
• Laboratory diagnosis is based on the finding of the oocysts in stool usually stained with a modified acid fast stain or a modified acid fast stain incorporated with iron haematoxylin.
• A study examining a number of asymptomatic children suggests laboratories be encouraged to include screening for C. parvum on a routine basis.(34)
• A study comparing three different stool concentration techniques, formalin-ether, sucrose density and zinc flotation indicate formalin ether to be the method of choice. They did however comment on the safety aspect of ether.(30) Click here for a demonstration. Full version only!
• Care must be taken to differentiate C. parvum in stool concentrate and smear from yeast, C. cayetanensis and debris. The technologist should be able to demonstrate the typical sporozoites in the oocysts.
• Note to physicians. In reference to the waterborne cryptosporidiosis outbreak in Milwaukee, Wisconsin 1993. It has been suggested that physicians should request Cryptosporidium testing for any patient with watery diarrhea.(31)

Click on the images below to enlarge.

Life Cycle

The mature oocysts is the infective stage and after ingestion by the host releases 4 sporozoites. The released sporozoites attach to the brush border of epithelial cells in the stomach and intestines. The sporozoites through the process of schizogony, produce a mature schizont which releases eight (8) first generation merozoites. It is these merozoites that invade the epithelial cells producing second generation schizonts. Four (4) second generation merozoites are then produced which further develop into micro or macrogametes. The macrogamete is fertilized by the microgamete. A zygote is produced which develops into the mature oocyst completing the cycle.

Back

Next

To Contents

The material on this site is owned by Scientific Image and Consulting
David M. Raymondo
MLT, CLS(m)
Professional Affiliation: Gamma-Dynacare Medical Laboratories, Ottawa, Ontario, Canada
Gamma-Dynacare is a Division of the Dynacare Health Group