As mentioned earlier, there are a large number of species of bird and non-human, mammalian schistosomes inducing allergic reactions and creating public health problems when invading human skin. In different regions, species of the following genera have been considered responsible for swimmers' itch: Austrobilharzia (Microbilharzia), Bilharziella, Gigantobilharzia, Heterobilharzia, Orientobilharzia, Schistosoma, Schistosomatium, and Trichobilharzia (Stunkard and Hinchcliffe 1952; Leigh 1955; Sahba and Malek 1979; Appleton and Randall 1986; McKown et al. 1991). The taxonomy of these parasites is not completely understood today (Farley 1971). Morphological and functional criteria applied for identification of the cercariae are swimming patterns and resting posture in the water, spination, size of the cercariae and proportional size of different organs of the larvae, number and organization of the penetration glands, structures of the excretory system (number of flame cells), localization of the sensory papillae, etc. (Nasir and Erasmus 1964; Farley 1971; Richard 1971; Blair and Islam 1983).

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