Parasites of the Class Trematoda (Phylum Platyhelminthes) are taxonomically diverse and largely consist of Subclass Monogenea, Aspidogastrea, and Digenea [1]. Only those of the Subclass Digenea are endoparasites of humans and animals. Species of trematodes important for human infections can be divided into four groups according to their habitat in the definitive host; blood flukes, liver flukes, lung flukes, and intestinal flukes (including those parasitic in the throat and pancreatic duct). Blood flukes comprise of more than five species of Schistosoma which parasitize in the mesenteric venules or vesical or pudental plexus of the urinary bladder [1]. The major liver flukes infecting humans include four species, Clonorchis sinensis, Opisthorchis viverrini, O. felineus, and Fasciola hepatica. They usually inhabit in the bile duct of humans or animals, although F. hepatica can also be found in ectopic foci such as the eye, intestinal wall, and muscles. More than eight species of Paragonimus are currently acknowledged to be able to infect the lungs of human patients; Paragonimus westermani, P. africanus, P. heterotremus, P. skrjabini, P. skrjabini miyazakii, P. kellicotti, P. mexicanus, and P. uterobilateralis [2]. Intestinal flukes are more diverse, including heterophyids (Metagonimus yokogawai, Heterophyes nocens, and Haplorchis taichui), echinostomes (Echinostoma revolu-tum, E. ilocanum, Echinochasmus japonicus, Artyfechinostomum malayatium, and Acanthoparyphium tyosenense), gymnophallids, lecithodendriids, microphallids, neodiplostomes, and plagiorchiids [3, 4]. Epidemiological characteristics of these trematodes that include the geographical distribution, prevalence and intensity of infection, mode of transmission and infection source, and others related to prevention and control are highly variable according to each trematode species (Table 8.1).
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