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Chapter 275 Cryptosporidium, Isospora, Cyclospora, and Microsporidia
Patricia M. Flynn
The spore-forming intestinal protozoa Cryptosporidium, Isospora, and Cyclospora are important intestinal pathogens in both immunocompetent and immunocompromised hosts. Cryptosporidium, Isospora, and Cyclospora are coccidian parasites that predominantly infect the epithelial cells lining the digestive tract. Microsporidia were formerly considered spore-forming protozoa and have recently been reclassified as fungi. Microsporidia are ubiquitous, obligate intracellular parasites that infect many other organ systems in addition to the gastrointestinal tract and cause a broader spectrum of disease.
Cryptosporidium is recognized as a leading protozoal cause of diarrhea in children worldwide and is a common cause of outbreaks in child-care centers; it is also a significant pathogen in immunocompromised patients.
Cryptosporidium hominis and Cryptosporidium parvum cause most cases of cryptosporidiosis in humans. Disease is initiated by ingestion of infectious oocysts that release 4 sporozoites that invade enterocytes, primarily in the small intestine. The infection progresses through 2 stages: the asexual stage, which allows autoinfection at the luminal surface of the epithelium, and the sexual stage, which results in production of oocysts that are shed in the stools. The cysts are immediately infectious to other hosts or can reinfect the same host.
Cryptosporidiosis is associated with diarrheal illness worldwide and is more prevalent in developing countries and among children <2 yr of age. It has been implicated as an etiologic agent of persistent diarrhea in the developing world and as a cause of significant morbidity and mortality from malnutrition, including permanent effects on growth.
Transmission of Cryptosporidium to humans can occur by close association with infected animals, via person-to-person transmission, or from environmentally contaminated water. Although zoonotic transmission, especially from cows, occurs in persons in close association with animals, person-to-person transmission is probably responsible for cryptosporidiosis outbreaks within hospitals and child-care centers where rates as high as 67% have been reported. Recommendations to prevent outbreaks in child-care centers include strict handwashing, use of protective clothes or diapers capable of retaining liquid diarrhea, and separation of diapering and food-handling areas and responsibilities.
Outbreaks of cryptosporidial infection have been associated with contaminated community water supplies and recreational waters in several states in the USA and the U.K. Wastewater in the form of raw sewage and runoff from dairies and grazing lands can contaminate both drinking and recreational water sources. It is estimated that Cryptosporidium oocysts are present in 65-97% of the surface water in the USA. The organism’s small size (4-6 µm in diameter), resistance to chlorination, and ability to survive for long periods outside a host create problems in public water supplies.
The incubation period is 2-14 days. Infection with Cryptosporidium is associated with profuse, watery, nonbloody diarrhea that can be accompanied by diffuse crampy abdominal pain, nausea, vomiting, and anorexia. Although less common in adults, vomiting occurs in >80% of children with cryptosporidiosis. Nonspecific symptoms such as myalgia, weakness, and headache also may occur. Fever occurs in 30-50% of cases. Malabsorption, lactose intolerance, dehydration, weight loss, and malnutrition often occur in severe cases. Recently, the clinical spectrum and disease severity has been linked with both the infecting species and host HLA class I and II alleles.
In immunocompetent persons, the disease is usually self-limiting, although diarrhea may persist for several weeks and oocyst shedding may persist many weeks after symptoms resolve. Chronic diarrhea is common in individuals with immunodeficiency, such as congenital hypogammaglobulinemia or HIV infection. Symptoms and oocyst shedding can continue indefinitely and may lead to severe malnutrition, wasting, anorexia, and even death.
Cryptosporidiosis in immunocompromised hosts is often associated with biliary tract disease, characterized by fever, right upper quadrant pain, nausea, vomiting, and diarrhea. It also has been associated with pancreatitis. Respiratory tract disease, with symptoms of cough, shortness of breath, wheezing, croup, and hoarseness, is very rare.
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