Cryptosporidium is a genus of protozoan parasites that are infectious to humans and animals. The first reports of human infection with Cryptosporidium were made in 1976; the infection occurs worldwide. Cryptosporidiosis, the enteric disease caused by Cryptosporidium is considered one of the most common parasitic infections in the United States. The largest water-borne outbreak occurred in Milwaukee, Wisconsin, in 1993, when more than 400,000 people were affected. People at highest risk are children less than two years of age, animal handlers, international travelers, homosexual individuals, health care and day-care workers, and the elderly. Cryptosporidiosis infections have been associated with drinking water, recreational water, contaminated food (mainly fruits and vegetables), and direct fecal local contamination.
There are many species of Cryptosporidium, and they infect a wide range of animals. Cryptosporidium parvum is the most common species infecting humans; however, rare cases of C. felis, C. canis, and C. meleagridis infections have been reported in persons with compromised immune systems. There are two main strains of C. parvum, one apparently restricted to humans (anthroponotic), the other infecting animals and humans (zoonotic). C. parvum can also infect humans, cattle, and other domestic animals.
Identification of Cryptosporidium is of both medical and veterinary importance. Cryptosporidium oocysts, the infectious stage of the parasite passed in the feces, predominantly colonize the epithelial cells of the small intestine—yet infections have also been found in epithelial cells of both the gastrointestinal and respiratory tract, including the bile ducts, gall bladder, pancreas, stomach, trachea, lungs, and possibly conjunctiva. Asymptomatic infections are common, though the most frequent symptom in humans is diarrhea. Symptoms often wax and wane, but generally remit in fewer than thirty days (with an average of one to two weeks) in most healthy, immunocompetent persons. Symptoms include profuse or watery diarrhea, dehydration, fever, anorexia, nausea, vomiting, stomach cramping, and flatulence. Immunocompromised persons often cannot clear the infection, which significantly contributes to such persons' illness and death.
Transmission routes are fecal-oral, person-to-person, animal-to-person, waterborne, and food-borne. Oocysts of C. parvum are round and 4 to 6 microns in diameter. They are so small that over 10,000 of them would fit on the period at the end of this sentence. The oocysts are highly resistant to chlorine, and to environmental conditions such as frost and heat.
In the laboratory, the most commonly used technique to detect Cryptosporidium oocysts in feces are staining procedures and commercial testing kits. Molecular methods of detection are mainly used as a research tool. Commercial blood tests are not yet available.
Various ways of preventing Cryptosporidium infection include educating the public in personal hygiene, using care in handling animal or human excreta, washing all vegetables and fruits, and avoiding drinking untreated water from lakes, rivers, springs, ponds, or streams. Ways of eliminating oocysts from drinking water are by boiling for one minute or by filter sterilization with either absolute 1.0 micron filters, reverse osmosis filters, or filters that meet NSF (National Sanitation Foundation) standards. Infected food handlers should be removed from work areas, and infected children should be excluded from day-care and recreational water facilities until the infection clears.
There is no established therapy for human cryptosporidiosis. Supportive measures to alleviate symptoms include antidiarrheal medication and management of fluid and electrolyte balance.
Bibliography
American Public Health Association (2000). "Control of Communicable Diseases Manual." 17:134–137.
Centers for Disease Control and Prevention (2000). Parasitic Pathways—Drinking Water. Available at http://www.cdc.gov/ncidod/dpd/parasiticpathways/drinkingwater.htm.
MacKenzie, W. R.; Hoxie, N. J.; Proctor, M. E.; Gradus, M. S.; Blair, K. A.; Peterson, D. E.; Kazmierczak, J. J.; Addiss, D. G.; Fox, K. R.; Rose, J. B.; and Davis, J. P. (1994). "A Massive Outbreak in Milwaukee of Cryptosporidium Infection Transmitted Through the Public Water Supply." New England Journal of Medicine 331:161–167.
— EVA M. KOVACS-NACE
