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Cryptosporidiosis

INTRODUCTION

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].

There are more than ten named species of Cryptosporidium, including species that infect mammals, birds, reptiles and fish [2]. C. parvum (4 mcm diameter) is the main species responsible for clinical disease in humans [3]. 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 only humans, while C. parvum is found in humans and a number of other animals [4,5].

C. felis, C. muris, C. canis, C. suis, and C. meleagridis have also been identified in some individuals [1,2,6]. Additional heterogeneity within species may lead to variations in infectivity and clinical expression in different hosts [7,8].

EPIDEMIOLOGY

Cryptosporidium was first identified as a cause of gastrointestinal disease in humans in 1976, and is now recognized globally as an important cause of diarrhea in both children and adults. Cryptosporidium has been described as the etiologic agent in three main epidemiologic scenarios [9]:

  • Sporadic, often water-related outbreaks of self-limited diarrhea in immunocompetent hosts
  • Chronic, life-threatening illness in immunocompromised patients, particularly those with HIV infection
  • Diarrhea and malnutrition in young children in developing countries
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