Itching and rash in a boy and his grandmother

Diagnosis: Scabies

The boy and his grandmother both have scabies, an infectious disease—in fact, the first human disease proven to be caused by a specific agent.¹Sarcoptes scabiei var hominis, or scabies, is a mite in the arachnid class.² In some states and localities, scabies cases or scabies outbreaks are reportable to the public health department.

The cardinal symptom of scabies is pruritus. The itch, especially with initial scabietic infestation, may be gradual in onset.³ Physical examination findings can vary from subtle and nonspecific to overwhelming and distinctive. Scabies can also mimic other dermopathies, complicating diagnosis. Undiagnosed and untreated, scabies can last a protracted period.

The dermopathy may be characterized by urticarial-type papules, vesicles, eczematoid change, excoriation, and bacterial superinfection, especially in children. Nodules may be present, particularly on the penis and scrotum. These may last for months after the infestation has cleared.³ The most commonly involved areas include fingers and finger webs, wrist folds, elbows, knees, the lower abdomen, armpits, thighs, male genitals, nipples, breasts, buttocks, and shoulder blades.^3,4 In young children, scabies may be found anywhere, including palms, soles, face and scalp.

Affliction of multiple family members and finding dermatitis in these distinctive locations is helpful in diagnosis. Finding the mites’ burrows is considered pathognomonic because other burrowing diseases (eg, cutaneous larva migrans) are easily distinguished clinically.⁴ Extensive excoriation is a clinical clue to look for burrows.³

Transmission usually skin-to-skin

Scabies is generally transmitted by prolonged skin-to-skin contact, such as occurs in families or during sexual contact. It is possible to acquire scabies infestation via contaminated items of clothing or bed linens, but this is not regarded as a significant route of transmission.³ Transmission by casual contact, such as a handshake or hug, is unlikely.

Infestation with the S scabiei mite, referred to as scabies in man, is termed “mange” in other mammals known to host the mite (dogs, cats, rabbits, cattle, pigs, and horses). Mites from one host species generally do not establish themselves on another species, and thus are referred to as varieties, variants, or forms. Humans develop a transient dermopathy from infestation by animal scabies, but such infestations are mild and disappear spontaneously unless the person is in frequent contact with the infested animal.^3,4