From Encyclopedia Jr, free information reference for Kids
Intestinal parasites are parasites that populate the gastro-intestinal tract. In humans, they are often spread by poor hygiene related to feces, contact with animals, or poorly cooked food containing parasites.
Three major groups of parasites include protozoans (organisms having only one cell), nematodes (roundworms), and cestodes (tapeworms). Of these, protozoans, including cryptosporidium, microsporidia, and isospora, are most common in HIV-infected persons. Each of these parasites can infect the digestive tract, and sometimes two or more can cause infection at the same time.
[edit] Infection
Parasites can get into the intestine through the mouth from uncooked or unwashed food, contaminated water, or hands, or by skin contact with larva infected soil. People can also become infected with intestinal parasites if they have mouth contact with the genital or rectal area of a sexual partner who is infected (e.g. oral sex or rimming). When the organisms are swallowed, they move into the intestine, where they can reproduce and cause disease.
[edit] Symptoms
In some people, intestinal parasites do not cause any symptoms, or the symptoms may come and go. Common signs and complaints include coughing, cramping abdominal pain, bloating, "gas" and diarrhea. In more serious infections, weight loss, skin-itching, fever, nausea, vomiting, or bloody stools may occur. Some parasites also cause low red blood count (anemia), and some travel from the lungs to the intestine, or from the intestine to the lungs and other parts of the body. Many conditions besides intestinal parasite infection can result in these symptoms, so laboratory tests are necessary to determine their cause.