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That amoebas cause disease must be an accident of nature. From all we know, amoebas can only be transmitted during the cyst stage. Cysts develop when amoebas that are able to reproduce and crawl inside the intestinal tract (trophozoites), are encapsulated by a thick layer of chitin, making them resistant to dryness, cold, and stomach acid, if they happen to be transmitted to another person through contaminated food or water. When causing disease, amoebas must be capable of migrating from inside the intestine into the intestinal wall, or of surviving in the bloodstream while being carried into the liver or in rare cases even into other organs. There is every indication that, once they have moved out of the intestinal duct, they are no longer able to form cysts. And even if they could, the cysts would certainly never be able to exit the organs. So the amoebas cannot longer be transmitted, and the capabilities of amoebas required to leave the intestinal duct and cause disease should have been lost in evolution long ago.
Molecules that are located at the surface of pathogens are of particular interest for the infection process. In pathogenic amoebas (Entamoeba histolytica), they influence the migration from the intestinal cavity into the tissues and the development of intestinal ulcers and organ abscesses.
Amoebas causing amoebic dysentery carry on their surfaces a substance that significantly enhances a specific immune reaction in the host. The substance is composed of an interesting combination of carbohydrates, peptides, phosphate residues and lipid chains.
Men suffer amoebic liver abscesses four times more frequently than women. This is also the case for the mice we use as models for human disease.
That it is the aggressive properties of amoebas (Entamoeba histolytic) which cause intestinal ulcers and abscesses in organs, has always been assumed and is reflected by the name “histolytica” – histos Greek for tissue and lysis for dissolution.
Amoebas (Entamoeba histolytic) possess an arsenal of digestive enzymes, including so-called peptidases or proteases. These are enzymes that cleave other proteins and so are able to digest them.
Studying mice we have found that amoebae, after leaving the intestinal tract and invading the tissue, may be recognized and killed by immune cells.