Cryptosporidium Parvum: Transmission and Infection

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Cryptosporidium Parvum: Transmission and Infection

Cryptosporidium parvum is a protozoan intestinal parasite causing a short-term enteric illness in individuals with functioning immune systems, and can cause a potentially fatal infection in immunosuppressed individuals. Because of C. parvum’s resistance to many of the procedures used to process drinking water and food, and the parasite’s extremely high fecundity, the potential for a large scale outbreak is very high. In fact, C. parvum was responsible for an outbreak in Milwaukee in 1993 when an estimated 403,000 people became ill. This was the largest waterborne outbreak of disease in United States history. This paper will cover some aspects of C. parvum’s life cycle, human sickness caused by the parasite, routes of transmission, and practices of control.

There are six different species of Cryptosporidium, C. parvum being the only species which infects mammals (Gutierrez, 1990). Oocysts, which are ingested by the mammal host, each contain four sporozoites. Upon excystment in the small intestine, the sporozoites infect an intestinal epithelial cell by becoming attached to the base of the microvilli. The sexual stages follow, where zygotes and eventually oocysts are formed. But C. parvum also has an “auto-infecting” asexual stage in which thin walled oocysts are produced to cause infection farther along in the intestine (Donnelly & Stentiford,1997). Approximately 20% of the oocysts produced will have these thin walls, leaving 80% of the oocysts to be excreted out of the host and into the environment, where they will be infective immediately. Thirty oocysts are enough to cause infection, and one infected person can excrete over a billion oocysts in one day (Graczyk et al., 2000).

Symptoms of Cryptosporidiosis in immunocompetent individuals include watery diarrhea (up to 3 liters a day), cramps, weight and appetite loss, nausea, vomiting and malaise (Gutierrez, 1990). Symptoms begin 3 to 5 days after the initial infection, and can last up to 2 weeks. Several relapses may occur due to the auto infecting mechanism of the parasite, but an otherwise healthy individual will rarely experience any more than 21 days of symptoms. Oocysts, however, may continue to be shed in the host’s feces for up to 2 months (Gutierrez, 1990).

Because there is no kno...

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...ter supplies and reserves for oocysts, and plans for containment in the event of an outbreak. Education of the public should also occur so that symptoms are reported in a timely manner to authorities so that, in case of an outbreak, measures could be taken to prevent further infection.

References

Donnelly, J.K., Stentiford, E.I. (1997) “The Cryptosporidium Problem in Water Food Supplies” Lebensm.-Wiss.U.-Technol., 30, 111-120

Graczyk, T.K., Evans, B.M., Shiff, C.J., Karreman, H.J. Patz, J.A. (2000) “Environmental and Geographical Factors Contributing to Watershed
Contamination with Cryptosporidium parvum Oocysts” Environmental Research Section A 82, 263-271

Graczyk, T.K., Fayer, R., Trout, J.M., Jenkins, M.C., Higgins, J., Lewis, E.J.Farley, C.A. “Susceptibility of the Chesapeake Bay to Environmental
Contamination with Cryptosporidium parvum” Environmental Research Section A 82, 106-112

Carpenter, C., Fayer, R., Trout, J., Beach, M.J., “Chlorine Disinfection of Recreational Water for Cryptosporidium parvum”
CDC Dispatch--- www.cdc.gov/ncidod/eid/vol5no4/carpenter.htm

Gutierrez, Yezid (1990) “Diagnostic Pathology of Parasitic Infections with Clinical Correlations” 94-107

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