Mites 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.
[...] Ectoparasites, ova, egg castings, feces, or pieces of mites are diagnostic. Norwegian scabies is a term describing a particularly severe form of scabies occasionally seen in senile and mentally impaired patients, those with debilitating illnesses, and immunosuppressed patients. Extensive crusting occurs, particularly of the hands and feet. Erythema and scaling may develop, and patients are literally "crawling with mites." This form of scabies is highly contagious resulting from the incredible number of mites on the patient and in the immediate vicinity. [...]
[...] Miscellaneous Mites Parasitiformes. This group contains gamasid mites that are parasites of birds, mammals, snakes, insects, and rarely, humans. In addition to being vectors of disease, gamasid mites are responsible for some cases of dermatitis. The chicken mite, Dermanyssus gallinae, is responsible for most of the dermatitis caused by this group. This pest of poultry is widespread and is associated with both domestic and wild birds. Poultry workers are common targets, but other persons may be infested from insidious sources, such as a pet canary or bird nest near an intake for ventilation or air conditioning. [...]
[...] Studies indicate that the dog scabies mites are able to survive for at least 96 hours on human skin, even burrowing and laying eggs, but whether a perpetual life cycle can be established is not yet determined. Infested dogs have reddish papules, scaling, crusting, and evidence of scratching. Humans develop itchy papules, often with some urtication, and scratching may give rise to varying degrees of secondary infection. The initial lesions are most often on areas of skin that come in contact with dogs: forearms, chest, anterior abdomen, and anterior thighs. [...]
[...] Snake mites have been implicated as a cause of dermatitis. Four members of one family developed a vesicobullous eruption from Ophionyssys natricis harbored by a pet python. Acariniformes. This huge group includes mites that infest foods, feathers, and furs. Individual infestations and larger outbreaks are common, with increased exposure by occupation, resulting in such terms as grocer's itch, miller's itch, and copra itch. Dogs, cats, and rabbits are primary hosts for mites of the genus Cheyletiella, and domestic pets are increasingly the source of mite dermatitis. [...]
[...] Clothing and linens should be laundered the morning after treatment to kill mites that may have strayed from the skin. When many members of a household are infested, live mites may be on the furniture; a-benzene hexachloride sprays are available. 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. An uncured case of Norwegian scabies as the focus of an epidemic may be surrounded by millions of mites. [...]
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