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These can be categorized into three groups; cestodes, nematodes and trematodes. Examples include: Acanthocephala; Ascariasis (roundworms) Cestoda (tapeworms) including: Taenia saginata (human beef tapeworm), Taenia solium (human pork tapeworm), Diphyllobothrium latum (fish tapeworm) and Echinococcosis (hydatid tapeworm)
Cestodes are parasites of vertebrates, with each species infecting a single definitive host or group of closely related host species. All but amphilinids and gyrocotylids (which burrow through the gut or body wall to reach the coelom [ 6 ] ) are intestinal, though some life cycle stages rest in muscle or other tissues.
Nematodes are very small, slender worms. Most are free-living, often less than 2.5 mm long and some only about 1 mm. Many nematodes are microscopic. Some soil nematodes can reach up to 7 mm in length, and some marine species can reach up to 5 cm. Some are parasitic and can reach lengths of 50 cm or more. [42]
There are 18,000 [1] to 24,000 [2] known species of trematodes, divided into two subclasses — the Aspidogastrea and the Digenea. Aspidogastrea is the smaller subclass, comprising 61 species. These flukes mainly infect bivalves and bony fishes. [3] Digenea — which comprise the majority of trematodes — are found in certain mollusks and ...
Trematodiasis is a group of parasitic infections caused by different species of flukes, in humans mainly by digenean trematodes. [4] Symptoms can range from mild to severe depending on the species, number and location of trematodes in the infected organism. [1]
[16] [17] Helminth eggs of concern in wastewater used for irrigation have a size between 20 and 90 μm and a relative density of 1.06–1.23. [18] It is very difficult to inactivate helminth eggs, unless temperature is increased above 40 °C or moisture is reduced to less than 5%. [ 18 ]
Some internal fish parasites are spectacular, such as the philometrid nematode Philometra fasciati which is parasitic in the ovary of female Blacktip grouper; [14] the adult female parasite is a red worm which can reach up to 40 centimetres in length, for a diameter of only 1.6 millimetre; the males are tiny.
In 2014–15, the WHO estimated that approximately 2 billion people were infected with soil-transmitted helminthiases, [6] 249 million with schistosomiasis, [60] 56 million people with food-borne trematodiasis, [61] 120 million with lymphatic filariasis, [62] 37 million people with onchocerciasis, [63] and 1 million people with echinococcosis. [64]