Parasitic worms, also known as helminths, are large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schistosomes reside in blood vessels.
Parasites are organisms that live in and feed off a living host. There are a variety of parasitic worms that can take up residence in humans. Among them are flatworms, roundworms, and thorny-headed worms (spiny-headed worms).
The risk of parasitic worm infection is higher in rural or developing regions. The risk is also greater in places where food and drinking water may be contaminated and sanitation is poor.

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