Human infestation caused by the Sarcoptes scabiei var. hominis mite that lives its entire life cycle within the epidermis.
Causes a diffuse, pruritic eruption after an incubation period of 4 to 6 weeks.
Is transmitted by close physical contact or by fomites.
Topical therapy with permethrin 5% cream is most effective topical therapy, but oral ivermectin, although off-label, is also effective.
Because of the common occurrence of asymptomatic mite carriers in the household, all family members and close contacts should be treated simultaneously.
Scabies is a worldwide issue that affects all ages, races, and socioeconomic levels. Prevalence varies considerably with some underdeveloped countries having rates from 4% to 100% of the general population.1 In the developing world the populations affected include children, the elderly, and immunosuppressed individuals. An infested host usually harbors between 3 and 50 oviparous female mites,2 but the number may vary considerably among individuals. For example, patients with crusted, formerly “Norwegian,” scabies (Fig. 178-1) who have a defective immunologic or sensory response (ie, leprosy, paraplegic, or HIV-infected patients) harbor millions of mites on their skin surface, with minimal pruritus. Infants and the elderly may not be effective scratchers and harbor intermediate numbers between 50 and 250 mites.
Crusted scabies. Hyperkeratotic plaques populated with thousands of mites.
It is well established that close personal contact is a prime route of transmission. Although sometimes considered a sexually transmitted disease, the equally high prevalence in children attests that close nonsexual contact among children and other family members is also sufficient to transmit the infestation. Transmission via inanimate objects has been best demonstrated with crusted scabies but is much less likely to occur in normal hosts. Crusted scabies is notoriously contagious, and anyone roaming within the general vicinity of these patients risks acquiring the infestation. Indeed, 6000 mites/g of debris from sheets, floor, screening curtains, and nearby chairs have been detected.3 Mites are also prevalent in the personal environment of normal scabies patients.4,5 In one study, live mites were recovered from dust samples taken from bedroom floors, overstuffed chairs, and couches in every patient’s dwelling.5
ETIOLOGY AND PATHOGENESIS
Scabies is an infestation by the highly host-specific mite, Sarcoptes scabiei var. homini, family Sarcoptidae, class Arachnida. The mite is pearl-like, translucent, white, eyeless, and oval in shape with 4 pairs of short stubby legs. The adult female mite is 0.4 × 0.3 mm with the male being slightly smaller—just slightly too small to be seen by the naked eye. The scabies mite is able to live for 3 days away from the host in a sterile test tube, and for 7 days if placed in mineral oil mounts.4,6 Mites cannot fly or jump.