Mites
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biology
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date published 20/11/2007
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SummaryMites make up the largest group in the class Arachnida. Most are small arthropods, and many are barely visible. Mites have two body regions, a small cephalothorax and a larger, unsegmented abdomen. The cephalothorax and abdomen are broadly joined, giving most mites an oblong to globular appearance. Newly hatched larvae have three pairs of legs, and larvae acquire a fourth pair after the first molt. Mites are highly diverse. Some are parasitic, with both vertebrates and invertebrates serving as hosts; some are scavengers, some feed on plants, and many are free living and predaceous. Although most species are oviparous, some are ovoviviparous, and a few are viviparous. They occur worldwide and frequently in great numbers. Mites have been associated with disease transmission, allergies, and dermatologic manifestations. Of the approximately 35,000 species, about 50 are known to cause human skin lesions, and most of the cutaneous lesions are caused by mites feeding or burrowing in the skin. Since children and adults of all races are susceptible to these ubiquitous arthropods, they are responsible for considerable morbidity. The mites of medical importance are some of the sarcoptic mites, some of the trombiculid mites, a number of other acariform mites that infest organic substances such as grains and produce, and the gamasid mites that are vectors of several rickettsial and viral diseases. Dermatologic manifestations of mite bites may be seasonal, as with the trombiculids; individual cases or outbreaks of varying magnitude may be related to contact with mites that infest animals or various foods. Epidemics may occur, as is presently the case with scabies.
Table of Contents
- The human scabies mite is Sarcoptes scabiei var. hominis, an obligate human parasite that completes its entire life cycle in and on the epidermis of humans.
- Severe nocturnal pruritus is the hall-mark of scabies. Itching also may be provoked by any sudden warming of the body and generally does not involve the face.
- Diagnosis is based on the combination of nocturnal pruritus and cutaneous findings and is confirmed by microscopic examination of burrow contents.
- A number of topical treatments are available. In most cases a single overnight application of 5% permethrin cream (Elimite) is curative.
- Control of scabies outbreaks in nursing homes and similar epidemic situations can be almost insurmountable because of the number of patients and contacts that must be treated simultaneously.
- Humans develop itchy papules, often with some urtication, and scratching may give rise to varying degrees of secondary infection.
- Treatment is symptomatic and consists of topical antipruritic agents, corticosteroids, systemic antihistamines, and occasionally, pulse therapy with systemic corticosteroids.
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