noun, singular: trematode infection
The trematodes (also called flukes) are a group of species belonging to the phylum Platyhelminthes, which are commonly called flatworms. The trematodes though are distinguished from other Platyhelminthes by their holdfasts resembling suckers. These suckers help them to anchor within their host. They are parasites of mollusks and vertebrates. There are two subclasses that comprise the trematodes, i.e. Digenea and Aspidogastrea. The subclass Digenea is the larger group and its members live as obligate parasites of both mollusks and vertebrates, including humans.
These flukes can also be classified according to the system of the vertebrate host that they infect. There are tissue flukes and blood flukes. The tissue flukes are parasitic trematodes that infest the lungs, bile ducts, and other tissues of their vertebrate hosts whereas the blood flukes are those that are found in blood. The vertebrate hosts are their definitive hosts and they are where the flukes sexually reproduce. The mollusks, usually snails, are their intermediate hosts and are from where the flukes reproduce asexually. Trematode infections in humans include Schistosoma, Clonorchis, Opisthorchis, Fasciola, and Paragonimus infections. They are common in Asia, Latin and South America, Middle East, and Africa. Schistosomiasis is a disease caused by Schistosoma (a blood fluke) infestation in the urinary or mesenteric blood vessels. Liver flukes, Clonorchis sinensis (causing clonorchiasis) and Fasciola hepatica, and lung fluke, Paragonimus westermani, are also capable of taking humans as definitive hosts.