Free-living protozoan groups that inhabit soils and natural waters are extremely diverse, not only in their structure but also in the manner in which they feed, reproduce, and move. The amoebas are a diverse group of free-living protozoa that probably evolved from a number of different primitive protozoan ancestors. The amoeboid group includes hundreds of different organisms, ranging in size from about .25 to 2.5 mm (about 0.0098 to 0.098 in). Amoebas are considered the most primitive animals and are classified in the kingdom Protista. All amoeboid organisms have thin cell membranes, a semirigid layer of ectoplasm, a granular, jellylike endoplasm, and an oval nucleus. Some species live on aquatic plants and some in moist ground; others are parasitic in animals and humans. At least six forms of amoeba are parasitic in humans. Most important of these is Entamoeba histolytica, which causes amebiasis and dysentery. The diseases often occur in epidemics when raw sewage contaminates water supplies or when soil is fertilized with untreated wastes. Amoebic dysentery is most commonly spread by water or contaminated, uncooked food or from carriers. Flies may carry the cysts to spread the amoeba from the feces of infected persons to food. In many publications Entamoeba histolytica is cited as infecting one tenth of the world population, or 500 million people. Life Cycle Diagram (Courtesy of the DPD)  Infection by Entamoeba histolytica occurs by ingestion of mature cysts  in fecal contaminated food, water, or hands. Excystation  occurs in the small intestine and trophozoites  are released, which migrate to the large intestine. The trophozoites multiply by binary fission and produce cysts  , which are passed in the feces. Because of the protection conferred by their walls, the cysts can survive days to weeks in the external environment and are responsible for transmission. (Trophozoites can also be passed in diarrheal stools, but are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment.) In many cases, the trophozoites remain confined to the intestinal lumen ( : non-invasive infection) of individuals who are asymptomatic carriers, passing cysts in their stool. In some patients the trophozoites invade the intestinal mucosa ( : intestinal disease), or, through the bloodstream, extra intestinal sites such as the liver, brain, and lungs ( : extra-intestinal disease), with resultant pathologic manifestations. It has been established that the invasive and non invasive forms represent two separate species, respectively E. histolytica and E. dispar, however not all persons infected with E. histolytica will have invasive disease. These two species are morphologically indistinguishable. Transmission can also occur through fecal exposure during sexual contact (in which case not only cysts, but also trophozoites could prove infective).
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Note: The statements contained on this website have not been reviewed or approved by the Food and Drug Administration for their validity. Nothing contained on this site is meant to infer or state that the products are for the treatment of any disease or ailment. Always consult with your physician if you experience any medical problems.
Source: Parasite images courtesy of the DPD
References and additional information:
- Centers for Disease Control & Prevention
- Howard Hughes Medical Institute
- Ohio State University, Biological Sciences
- Skye Weintraub, ND "The Parasite Menace""; Woodland Publishing 2000
- Ann Louise Gittleman, MS, CNS "Guess What Came To Dinner?"; Avery 2001
- Valerie Saxion "Everybody Has Parasites"; Bronze Bow Publishing 2003
- Skye Weintraub "The Parasite Menace"; March 1998
- Roger M. Knutson "Fearsome Fauna: A Field Guide to the Creatures That Live in You"
- Carl Zimmer "Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures"
- Paavo Airola, ND, PhD "How To Get Well"; Health Plus Publishers
- Nicholas Culpepper "Culpepper's Complete Herbal"; Omega 1985
- Penny C. Royal "Herbally Yours"; Sound Nutrition 1982
- James F. Balch, MD "Prescription For Nutritional Healing"; Sound Nutrition 1997
- Alma R. Hutchens "Indian Herbology of North America"; Merco 1973
- Discover Magazine; August 2000 Edition
- Centers for Disease Control & Prevention
- Howard Hughes Medical Institute
- Ohio State University, Biological Sciences
- Skye Weintraub, ND "The Parasite Menace""; Woodland Publishing 2000
- Ann Louise Gittleman, MS, CNS "Guess What Came To Dinner?"; Avery 2001
- Valerie Saxion "Everybody Has Parasites"; Bronze Bow Publishing 2003
- Skye Weintraub "The Parasite Menace"; March 1998
- Roger M. Knutson "Fearsome Fauna: A Field Guide to the Creatures That Live in You"
- Carl Zimmer "Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures"
- Paavo Airola, ND, PhD "How To Get Well"; Health Plus Publishers
- Nicholas Culpepper "Culpepper's Complete Herbal"; Omega 1985
- Penny C. Royal "Herbally Yours"; Sound Nutrition 1982
- James F. Balch, MD "Prescription For Nutritional Healing"; Sound Nutrition 1997
- Alma R. Hutchens "Indian Herbology of North America"; Merco 1973
- Discover Magazine; August 2000 Edition
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