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The amoeba and ciliates are protozoan parasites that have been causing illness in humans since antiquity. The most relevant foodborne parasites of these groups are Entamoeba histolytica and Balantidium coli. Entamoeba dispar has been identified mostly in asymptomatic patients however, reports demonstrating invasive amebiasis caused by E. dispar may indicate various levels of pathogenicity. In recent years, studies on the pathogenesis and immune responses to amoebiasis are providing insights on how to control this parasitosis that affects more than 50 million people annually.This chapter will address the various aspects of these parasites, from the biology, life cycle, clinical presentation, and treatment.

Protozoan parasites were the most frequently identified etiologic agents in waterborne disease outbreak from 1991 to 1994. The waterborne parasites Giardia lamblia, Naegleria fowleri, Acanthamoeba spp., Entamoeba histolytica, Cryptosporidium parvum, Cyclospora cayetanesis, Isospora belli, and the microsporidia are reviewed. For each parasite, the review includes history, life cycle, incidence, symptoms, and therapy. Clinical detection methods are compared, and emerging technologies are discussed. Information on the association of these parasites with waterborne outbreaks is reviewed. Current information on protozoan parasites identified as etiological agents in waterborne outbreaks is discussed. Water industry issues related to recent disease outbreaks are examined in the context of water quality testing regulations for G. lamblia and those proposed for C. parvum. The review identifies the limitations of the American Society of Testing and Materials water-testing method for these parasites. An overview of federal regulations affecting the water industry and laboratories that test for water quality is also provided. The article highlights the importance of the clinical laboratory as a frontline defense for the detection of infectious organisms. The review points to the need for clinical laboratories, physicians, and public health personnel to cooperatively plan and assess the challenge of meeting this potential public health threat.