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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.
They are larger than bacteria and viruses but usually so small that you cannot see them without a microscope. 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.
How do people become infected?
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.
What are the signs of intestinal parasite infection?
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, 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.
Intestinal parasites can infect anybody. However, HIV-infected persons may not be able to control parasite infection very well if they have advanced disease. Under these circumstances, intestinal parasite infection may become a long term health problem.
- intestinal nematodes (intestinal roundworms)
- Ascaris lumbricoides: ascariasis
- Ancylostoma duodenale
- Necator americanus
- Strongyloides stercoralis: strongyloidiasis
- Trichiuris trichiura: whipworm, trichuriasis
- Trichostrongylus species: trichostrongyliasis
- Anisakis simplex, Pseudoterranova decipiens: anisakiasis
- Capillaria philippinensis: capillariasis
- intestinal cestodes (flatworms)
- Taeniasis solium: tapeworm
- intestinal protazoa
- agents transmitted by fecal-oral route but not properly intestinal parasite
- foodborne illness
- CDC pages on the morphology of intestinal parasites
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