Infections by the protozoan parasites of the genera Cryptosporidium and Giardia can be asymptomatic or cause gastroenteritis in immunocompetent people. However, in immunocompromised individuals, the infections can be more severe and even life threatening. Both parasites are common waterborne pathogens, but on occasion they may be foodborne or transmitted by body contact. In this review, several aspects of Cryptosporidium and Giardia are discussed including their life cycles, resistance to physical and chemical agents, routes of transmission to humans, the nature of the disease caused by the parasites, and detection of the organisms in water, feces, and food. Documented incidents in which Cryptosporidium or Giardia contaminated foods were implicated as cause of gastroenteritis are discussed to illustrate conditions leading to foodborne outbreaks and to suggest means of prevention and control of the parasites when present in foods.
Resistance of pathogenic Naegleria to some common physical and chemical agents.
