Parasites as pathogens
The true definition of a parasite is an organism that lives on or in another organisms, deriving benefit from it but providing nothing in return.
Nor all ‘parasites’ cause disease; organisms such as Entamoeba dispar, a protozoan, live in the human gut without causing disease and are thus colonizers.
Around 500 million individuals in the world are infected with amebiasis caused primarily (90%) by E. dispar.
This closely related species E. histolytica is capable of invading the bowel wall, causing colitis and abscesses in the liver, brain and other tissues.
E. histolytica is a powerful pathogen that uses proteases to destroy hosts’ tissues, kill some hosts’ cells and “phagocyte” red cells.
Multicellular parasites such as schistosomes may also be pathogens. In the past, diseases caused by metazoan parasites, such as schistosomiasis, were sometimes called infestations. Nowadays all parasitic diseases are called infection.
Parasites as pathogens
