Acari mites and ticks

Non-insect arthropods of great medical importance in the northern Holarctic region include several groups of ectoparasitic mites, for example, the minute chigger mite larvae (Leptotrombidium, Neotrombicula) as well as endoparasitic mites (e.g. Sarcoptes scabiei) and the larger ticks (Ixodidae, Argasidae). Mites and ticks (Acari) belong to the class of arthropods denoted as Arachnida. The scorpions, harvest-men, and true spiders also belong to the arachnids. About 30000 species of mites and 800 species of ticks have been described, but about half a million species of mites are believed to exist (Varma 1993). Most Acari, except the nymphs and adults of most ticks, are very minute animals and should preferably be studied with a compound or scanning electron microscope. Nearly all mite species lay eggs. The egg develops to a six-legged larva, which then becomes an eight-legged nymph. Depending on the species there may be one or several nymphal stages. The life-cycle in some species can be as short as one week but in other species (argasid ticks) can be a decade or more. Infestation by mites is termed acariasis. Mites can be medically important because they ingest blood, lymph, or dermal tissues, because they may cause dermatitis or other tissue damages, or cause serious allergic reactions, and/or because they can transmit pathogenic microparasites (from wild or domesticated vertebrates) to man. In the following sections, the Acari has been denoted as: (i) ectoparasitic mites; (ii) endoparasitic mites; (iii) soft ticks; and (iv) hard ticks. It should be emphasized that the first two groups are not taxonomic entities, but only an artificial way of treating a number of taxonomically diverse mite taxa into two groups based on their way of living on or inside the host, respectively.

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