Which of the parasitic worms has only one host?

Many parasitic worms need to change two or even three hosts to continue their cycle. And only the development of human roundworm occurs without a change of owners. Ascaris parasitizes in the small intestine, but the larvae during migration can enter other organs of the body. The reasons for infection with this type of helminths can be the consumption of unwashed food (especially fruits and vegetables) and contact with a person infected with roundworms. The main way to prevent infection with helminths is to observe personal hygiene.