Medically important parasitic arthropods insects ticks and mites of the northern Holarctic region

Thomas G. T. Jaenson

Medical entomology is the science about the arthropods, that is, insects, arachnids, and related evertebrates, which cause human disease. It is a very vast and important biomedical discipline encompassing subjects such as entomology, ecology, epidemiology, infectious disease control, and environmental science including the science about the conservation of nature and natural resources. In the following brief account, I will focus on the main features concerning the biology and medical importance of the taxa (taxonomic groups) of parasitic arthropods which are of outstanding significance to human health in the northern parts of the Holarctic (Palaearctic and Nearctic) zoogeographical region. A parasite can be defined as an organism living in or on another organism, its host, from which the parasite obtains food. Parasites living inside the host are denoted as endoparasites (e.g. myiasis-causing fly larvae, and Sarcoptes and Demodex mites) while parasites living on the host are termed ectoparasites. Ectoparasites are arthropods which spend the whole or a great part of the life-cycle on the host. They may be subdivided into host ectoparasites, nest ectoparasites, and field ectoparasites. Host ectoparasites, for example, blood-sucking lice (Anoplura), spend the whole life-cycle on the host. Nest ectoparasites (e.g. soft ticks (Argasidae), fleas (Siphonaptera), and bed bugs (Heteroptera: Cimicidae)) spend all stages in the vicinity of the host on which one or several of the active stages take blood. Most species of hard ticks (Ixodidae) can be denoted as field ectoparasites; they spend most of their life away from the host but when a host has been encountered the tick usually spends several days attached to its skin until fully engorged (Nelson et al. 1975).

Due to limitation of space, medically important blood-sucking Diptera such as mosquitoes (Culicidae), black-flies (Simuliidae), biting midges (Ceratopogonidae), horse-flies, deer flies and clegs (Tabanidae), stable-flies and horn-flies (blood-sucking Muscidae), and louse-flies (Hippoboscidae) are not treated in this chapter. In a broad parasitological sense, the blood-sucking adult sex(es) of these Diptera may be regarded as temporary, blood-feeding ectoparasites. However, in a stricter sense, they may not be regarded as ectoparasites. Further information on ectoparasitic and endoparasitic arthropods of medical and veterinary importance can be obtained from Smart (1948), Gordon and Lavoipierre (1972), Smith (1973), Harwood and James (1979), Alexander (1984), Jaenson (1985), Lane and Crosskey (1993), Kettle (1995), and Wall and Shearer (1997) and from references provided in these books. Very useful are also the publications and unpublished documents on vector biology and control from the World Health Organization (WHO) and the Pan American Health Organization (PAHO). In order to follow the most recent research on ectoparasitic and endoparasitic arthropods the following monthly journals are highly recommended: The Journal of Medical Entomology, Medical and Veterinary Entomology, and The Review of Medical and Veterinary Entomology.

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