Life cycles for parasites.

Arctic Biodiversity Assessment (ABA) 2013.

Figure 15.1. Life cycles for parasites.

Transmission patterns emphasize the triad of ‘host-parasite-environment’, thus both biotic and abiotic mechanisms and controls serve to determine the occurrence of helminths, arthropods, protozoans and viruses. Indirect cycles involving development of larval stages in intermediate hosts ( IH-1 to IH-3) are typical for most helminth parasites in terrestrial, freshwater and marine systems of the Arctic. The IH(s) in specifi c cycles are usually invertebrates (arthropods, molluscs, annelids) or occasionally other vertebrates (fi shes, birds or mammals) that are important as prey for the defi nitive or fi nal host. Among helminths, 1-3 intermediate hosts are often required for transmission, and the length of the cycle is characteristic of a particular parasite group. In these cases life cycles describe predictable pathways associated with trophic linkages, and thus parasites serve as ecological indicators for diet or other host activities. Indirect cycles may also involve arthropod vectors ( V-1) that are required for development and transmission of parasites to the fi nal host, usually for macroparasites or microparasites in the blood. Direct cycles involve transmission between defi nitive hosts, often with infective stages distributed in the environment.

Photo: Matakiel Island, Northern Sea of Okhotsk, by E.P. Hoberg.

Conservation of Arctic Flora and Fauna (CAFF)

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Meltofte, H. (ed.) 2013. Arctic Biodiversity Assessment. Status and trends in Arctic biodiversity. Conservation of Arctic Flora and Fauna, Akureyri.