Human parasites are parasitic organisms that need to live in a human body, where they're called endoparasites, or on the skin of a human body, where they're called ectoparasites. A human parasite gets all of its nourishment from the human body upon which it feeds, which is commonly referred to as the host. In many cases, a parasite can't live without the host. Some common endoparasites include certain types of roundworms, flatworms, and amoebas or protozoa. Examples of ectoparasites include lice, scabies, and bedbugs.
Eterobius follicularis, more commonly known as the pinworm or threadworm, is considered to be one of the more common human parasites. This intestinal parasite takes up residence in the host's colon and mates. After mating, the male of the species usually dies and is passed out of the body in the stool.
After her body fills with eggs, the female pinworm makes her way down the colon and eventually out of the host's body. Before dying, she deposits her eggs on and around the anus, which typically results in the intense itching associated with pinworm. A person usually contracts these worms by ingesting the eggs. Children are at a considerably higher risk than adults of getting pinworm, due to their lackadaisical approach to hygiene.
The tapeworm, of the genus Taenia, is a type of flatworm that is usually ingested by someone eating contaminated pork or beef. These human parasites are thought to be the world's longest parasite, and one record tapeworm, measuring 37 feet (11.3 meters), was removed from a woman through her mouth. These parasites usually attach their heads to the intestinal wall, leeching off of the host's nutrients. Another common parasitic flatworm that can infect a human is the liver fluke, or Clonorcis sinensis. Unlike the tapeworm, this parasite feeds off of and burrows into the hosts liver, and it is usually contracted from ingesting contaminated water or undercooked fish.
Giardia lamblia is another very common human parasite. This tiny, single-celled organism usually takes up residence in a human host's small intestine, but it can be found in other animals as well. It can cause a number of gastrointestinal problems, including severe diarrhea, gas, abdominal pain or discomfort, and nausea. This parasite is usually present in fecal matter of infected people, and can be spread through contaminated water or, sometimes, unsafe or unclean sexual practices.
Bedbugs and scabies are ectoparasites, as are head, body, and pubic lice. Each of these human parasites feeds off of the host's blood, and, as a result, the infested areas of the body are usually very itchy. Most of these types of human parasites are usually spread by contact with affected people or materials, such as bed sheets or hair brushes.