BIOLOGY Lecture Notes - Golden Pages 2003

10. MEDICAL PARASITOLOGY

Classification of Parasitism

From the perspective of a parasitic lifestyle, a distinction is made between true and false parasitism, as well as obligatory and facultative forms.

True parasitism occurs when the relationship between the parasite and the host is regular and has an evolutionary basis.

False parasitism occurs when, under normal conditions, a given parasite species leads a free-living existence. Upon entering a host Organism, a false parasite may remain viable for a certain period and disrupt the host's normal functioning.

Obligate parasitism is parasitism that is essential for a given species of organisms. The majority of parasite species belong to this group.

Facultative parasites can lead a free-living lifestyle, but upon entering a host organism, they complete a part of their developmental cycle within it and disrupt its normal physiological Functions.

Temporary parasites visit the host solely for feeding purposes (primarily Blood-sucking Arthropods).

Permanent parasites are divided into stationary and periodic ones.

Stationary parasites spend their entire lives on or inside the host. Examples include lice, the itch mite, Trichinella spiralis, and others.

Periodic parasites spend a part of their life cycle in a parasitic state while living freely the rest of the time. For instance, the Strongyloides stercoralis.

It is not uncommon for only the larval stages to lead a parasitic lifestyle, whereas the sexually mature forms live freely. Such larval parasitism is referred to as larval parasitism. The opposite phenomenon, where the larva is free-living and the sexually mature adult lives as a parasite, is termed imaginal parasitism.

Of particular importance in medicine is the Classification of parasites based on their localization within the host organism.

Ectoparasites reside on the integument of the host. These include blood-sucking insects and mites.

Endoparasites inhabit the interior of the host. They are subdivided into parasites living in hollow Organs communicating with the external environment (digestive, respiratory, and urogenital systems) and parasites of the internal milieu Tissues (Musculoskeletal System, blood system, and Connective Tissue).

During their life activity, parasites frequently migrate within the host organism and are thus capable of initially inhabiting hollow organs before moving into the body tissues (Example: Trichinella and the pork tapeworm).