Worms are a parasite we don't typically asspciate with humans in this day and age. While we almost expect our dogs, horses and cats to suffer from them, the fact remains that people are animals too and there are a wide variety of worms that would love to make their home inside the human body.
The most common form of worm that can be found in the human body is the pinworm. Pinworms live inside the colon but leave to lay their eggs on the outside of the host's body, typically at night in a location the host will reflexively scratch, thus transporting the eggs to infect a new person, or reinfect the host.
Hookworms are a particularly nasty parasite that actually has teeth, according to Allergyescape.com. Infection can be caused by consuming compromised fruit or water, or by coming into contact with soil or water where the worms reside. This parasite lives in the intestine, where it drinks blood.
Another common type of worm that can make its home in the human body is the roundworm. Infected soil or fruits are the main method of transmission to humans. Unlike most other worms, Roundworm eggs can find their way from the intestines to other organs where they can do major damage.
One of the more well known parasites, tapeworms are commonly found in cats and dogs, but have been known to make their home in humans as well. Undercooked fish is one potential cause of transmission. This parasite feeds by attaching itself to the wall of the intestine where it lives off nutrients that the body absorbs.
Liver flukes make their home in the human body where they attack the liver and make holes. They can survive for decades. There is a wide variety of methods of becoming infected by a liver fluke, including eating contaminated food, or drinking contaminated water.