Larry G. Arlian
The Acari (mites and ticks) represent a large array of organisms that exhibit very diverse lifestyles. This article deals with the acarines that are of importance to human health, a group that includes human parasites, natural parasites of other mammals and birds that in particular situations may bite humans, and acarines whose fecal matter, body secretions, and disintegrating bodies are sources of potent allergens.
The parasitic Acari of vertebrates are physiologically dependent on their host and must obtain nourishment from tissue fluids, blood, and cytoplasm from the host to survive, complete the life cycle, and reproduce. Thus, these are obligate parasites. Some species are temporary parasites (e.g., ticks), which visit and feed on the host intermittently. In contrast, other species of parasitic Acari (e.g., scabies and follicle mites) are permanently associated with the host and perish if they become separated from the host. For some species, only one life stage in the life cycle is a parasite (e.g., chiggers), whereas for other species each life stage must feed from a vertebrate host to complete the life cycle (e.g., scabies mites and ticks).
There is usually an intimate interrelationship between acarine parasites and their hosts. Specific host factors, such as carbon dioxide, body odor, and temperature, allow the parasite to locate a host. For example, scabies mites are attracted to the host by body odor and temperature. Permanent parasites may be directed to specific areas of the host body by factors in the skin. The host-parasite interactions for most parasitic acarines have not been well studied and thus are not well understood. This article discusses mites that bite humans, live in the skin of humans, or produce substances that induce immune and/or inflammatory reactions. Because acarine parasites can induce inflammatory and adaptive immune responses, an understanding of the relationship between these two responses is important if one is to understand the symptoms associated with bites from parasitic mites or reactions to body parts, secretions, and fecal matter.
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