Dermatosis caused by arthropods

HUMAN SCABIES. {Fig 35-9; see Fig 22-1). This disease is usually transmitted through prolonged personal contact with infected people and less often by clothing and bed linens. The mite's location is in a "burrow" in the stratum corneum where it deposits its eggs. An allergic sensitization to the mite and or its products causes the clinical picture. Itching appears 2 to 4 weeks after the infestation and is classically more severe at night. As a clinical finding the burrow is pathognomonic and diagnostic. The remaining lesions are secondary to scratching, secondary infections, and allergic reaction.

Methotrexate Skin Rash Pictures

The burrow is a skin-colored, tortuous, elevated line of 1 to 1.5 cm in length. They are usually found in the finger webs, flexor surface of the wrist, nipples, and elbows. In children, they are common in the palms and soles. The diagnosis is confirmed by a potassium hydroxide (KOH) preparation of the skin and the identification of the parasite. For treatment, permethrin 5% solution, one 8-hour application at night, is considered the standard treatment today. The gamma isomer of hexachlorobenzene (Lindane), 1% in a vanishing cream, was used for years, but it is used less commonly today because of its toxicity and should not be used in pregnant women and infants. With both medications a second application is made after 1 week. Note that this application should cover the entire body very thoroughly. A 6% sulfur precipitate in Vaseline for three consecutive days is employed in infants and pregnant women. Recently, ivermectin 200 micrograms per kilo, in a single dose, has been found to be very effective, but its safety is questioned by some authors. The nails should be cut short and scrubbed vigorously. Clothing and bed linen should be washed thoroughly. Norwegian scabies is the same disease but in an immunosuppressed individual. Typically, extensive, crusted, hyperkeratotic plaques are seen and itching may not be as prominent. The KOH examination shows a very severe infestation, and the patient is much more contagious. Treatment should include exfoliatives such as 20% urea or 20% salicylic acid in an ointment form.

Nodular scabies consists of brown or red firm nodules on the penis, scrotum, or buttocks and may persist for months despite specific antimite treatment. It is a delayed allergic reaction with no mite present.

ANIMAL SCABIES. In this disease, very similar to papular urticaria, the mites invade human skin, but they do not become established in it. There are varieties from dogs, sheep, birds, and so forth. Excoriated, crusted papules can be seen and pruritus can be very severe especially in the evening.

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