- Amoebae are structurally simple protozoa which have no fixed shape.
- The parasitic amoebae inhabit the alimentary canal.
Parasitic amoebae belong to the following genera:
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Entamoeba histolytica is an important human pathogen, causing amoebic dysentery as well as hepatic amoebiasis and other extraintestinal lesions.
E.hartmanni is nonpathogenic, though it resembles E. histolytica very closely except for its smaller size and was therefore known as the ‘small race’ of E. histolytica.
E.polecki a natural parasite of pigs and monkeys may sometimes infect humans causing diarrhoea.
E. coli is a common commensal in the colon and its importance is that it may be mistaken for E.histolytica.
E.gingivalis is present in the mouth, being found in large numbers when the oral hygiene is poor. It has no cystic stage and so the trophozoites depend for transmission on direct oral contact as in kissing, air-borne spread through
salivary droplets and fomites such as shared drinking and eating utensils. It is generally nonpathogenic, though it has been claimed that it contributes to periodontal disease.
All the genera of intestinal amoebae other than Entamoeba are nonpathogenic commensals, except D.fragilis, which may occasionally cause chronic, but mild intestinal symptoms. Intestinal amoebae can be differentiated based on their morphological features.