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Epidemiology, clinical manifestations, and diagnosis of cryptosporidiosis

Karin Leder, MBBS, FRACP, PhD, MPH, DTMH
Peter F Weller, MD, FACP
Section Editor
Edward T Ryan, MD, DTMH
Deputy Editor
Jennifer Mitty, MD, MPH


Cryptosporidium is an intracellular protozoan parasite that is associated with gastrointestinal diseases in all classes of vertebrates including mammals, reptiles, birds, and fish. Along with Giardia, it is among the most common parasitic enteric pathogens in humans. The organisms infect and reproduce in the epithelial cells of the digestive or respiratory tracts. Infection is predominantly associated with diarrhea and biliary tract disease [1].

This topic will review the epidemiology, clinical manifestations, and diagnosis of cryptosporidiosis. The treatment and prevention of cryptosporidial disease are found elsewhere. (See "Treatment and prevention of cryptosporidiosis".)


Over the last few years molecular methods have enabled characterization and identification of species and genotypes within Cryptosporidium isolates [2]. There are about 20 species of Cryptosporidium, including species that infect mammals, birds, reptiles, and fish [3]. C. parvum (4 mcm diameter) is the main species responsible for clinical disease in humans [4]. C. parvum has been divided into two separate species: C. hominis (previously C. parvum genotype 1) and C. parvum (previously C. parvum genotype 2). C. hominis apparently infects mainly humans, while C. parvum is frequently found in a number of other animals as well as in humans [5,6].

The host range for many species seems to be quite variable, and C. felis, C. muris, C. canis, C. suis, and C. meleagridis have also been identified in some individuals [1,3,7]. Additional heterogeneity within species may lead to variations in infectivity and clinical expression in different hosts [8,9].


Overview — Cryptosporidium was first identified as a cause of gastrointestinal disease in humans in 1976. Cryptosporidium species have been identified in every continent except Antarctica [10], and are now recognized globally as an important cause of diarrhea in both children and adults [11,12]. Cryptosporidium has been described as the etiologic agent in three main epidemiologic scenarios [13]:


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