الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Free living amoebae (FLA) are unicellular protozoa that are common in most aquatic environment (Page, 1988). FLA are distinct from other parasitic protozoa due to their free-living existence. They have been isolated from air, soil, and water samples throughout the world (Gutierrez, 2000). They exist in nature without the need for a host; they are not well adapted to parasitism and do not require a vector for transmission to humans or animals (Schuster and Visvesvara, 2004a). Of the many hundreds of species of FLA, few members including the genera Acanthamoeba, Naegleria fowleri, Balamuthia mandrillaris and Sappinia diploidia are known to infect humans, often with fatal consequences. These opportunistic parasites can infect humans and other mammals and cause serious eye or brain infection (Schuster and Visvesvara, 2004b). All of these species cause central nervous system (CNS) infections, but several species of Acanthamoeba may cause localized extra-CNS infections in immunocompetent hosts or disseminated infections in immune- compromised hosts (Heelan and Ingersoll, 2002). Their presence depends first of all on sufficient moisture in a habitat, but it is also dependant on other factors, such as chemical conditions and temperature (Mrva, 2003). Infections have become increasingly common with the emergence of AIDS and immunosuppressive agents. They play therefore an important role in the multiplication and dispersal of their facultative parasites. They are also related to some diseases in aquatic organisms (Dykova et al., 1999). Free-living amoebae have gained increasing attention from the scientific community due to their diverse roles, in particular in causing serious and sometimes fatal human infections. Because of all these threats and their possible impact on human and animal health, it is important not only to be able to detect but also to quantify the density of these pathogenic FLA in human-exposed aquatic environments (Schuster and Visvesvara, 2004a).