Helminths

Helminths (/ˈhɛlmɪnθs/), also commonly known as parasitic worms, are large multicellular organisms, which when mature can generally be seen with the naked eye. They are often referred to as intestinal worms even though not all helminths reside in the intestines; for example schistosomes are not intestinal worms, but rather reside in blood vessels.

There is no clear consensus on the taxonomy of helminths; it is more of a commonly used term to describe certain worms with superficial similarities. These are flatworms (plathelminths), namely cestodes (tapeworms) and trematodes (flukes), and roundworms or nemathelminths (nematodes) - both of these are parasitic worm types – and the annelida, which are not parasitic or at the most ectoparasites like the leeches.

Many, but not all, of the worms referred to as helminths belong to the group of intestinal parasites. An infection by a helminth is known as helminthiasis, soil-transmitted helminthiasis, helminth infection or intestinal worm infection. The same naming convention applies to all helminths whereby the ending "-asis" (or in veterinary science the ending "-osis") at the end of the name of the worm is added to signify the infection with that particular worm, for example Ascaris is the name of a particular helminth, and ascariasis is the name of the infectious disease caused by this helminth.