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12
Trematodes: Flukes

General Characteristics

Trematodes are unsegmented helminths, flat, broad and leaf shaped. They have
large prominent suckers. Trematodes are hermaphrodites except for schisto-
somes. Their eggs are operculated except for schistosome eggs. Snails are the
only intermediate host for schistosomes and are the first intermediate host for
other trematodes. Metacercaria is the infective stage for trematodes except for
schistosomes whereby cercariae is the infective stage. Trematodes are classified
as in Table 12.1.

Table 12.1 Classification of trematodes of medical importance based on habitat
Habitat Trematode
Blood Blood fluke
1. Schistosoma haematobium (In the vesical and pelvic venous plexuses)
2. Schistosoma mansoni (In the inferior mesenteric vein)
3. Schistosoma japonicum (In the superior mesenteric vein)
Biliary tract Liver fluke
1. Clonorchis sinensis
2. Opisthorchis viverrini
3. Fasciola hepatica
Intestine Intestinal fluke
1. Fasciolopsis buski
2. Heterophyes heterophyes
3. Metagonimus yokogawai
Respiratory tract Lung fluke
1. Paragonimus westermani

© Springer International Publishing AG 2017 135
R. Mahmud et al., Medical Parasitology,
https://doi.org/10.1007/978-3-319-68795-7_12