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Emergency and Acute Medicine - Scabies
Scabies (Sarcoptes scabiei infestation)
Scabies is a parasitic skin infestation caused by the mite Sarcoptes scabiei var. hominis. The mites live on the skin surface, where the fertilized female burrows into the stratum corneum to lay eggs. The hallmark symptom—intense itching (pruritus)—is not due to the mites themselves but results from a delayed type IV hypersensitivity reaction to mite proteins, eggs, and fecal material. This explains why symptoms often appear 10–30 days after initial infestation, but much faster (1–3 days) with reinfestation. Although scabies has existed for thousands of years, it remains a major global health problem, particularly in crowded and resource-limited settings.
Transmission occurs mainly through prolonged skin-to-skin contact (15–20 minutes), making it common among household members, sexual partners, and institutionalized populations. Indirect spread via clothing or bedding is less common but possible because mites can survive up to 3 days off the human body. Importantly, scabies is associated more with overcrowding than poor hygiene. Most individuals harbor only 5–15 mites, but in crusted (Norwegian) scabies, seen in immunocompromised or debilitated patients, there may be thousands to millions of mites, making it highly contagious.
Clinically, patients present with generalized itching that worsens at night, often with minimal visible findings. The classic lesion is a burrow—a thin, linear, grayish track—commonly found in the finger web spaces, wrists, elbows, waistline, axillae, buttocks, and genitalia. Secondary lesions such as papules, nodules, excoriations, or superimposed bacterial infection are often more prominent than the burrows themselves. In adults, the face and scalp are usually spared, whereas infants and young children may have widespread involvement including the face, scalp, palms, and soles, often with vesicular or bullous lesions. Crusted scabies presents differently, with thick hyperkeratotic plaques, scaling, and minimal itching despite heavy infestation.
Diagnosis is primarily clinical, based on history of pruritus, typical lesion distribution, and possible contact exposure. Skin scraping of burrows examined under microscopy may reveal mites, eggs, or fecal pellets, but sensitivity is low (<50%), so a negative test does not exclude the diagnosis. In endemic settings, empiric treatment is often reasonable. Advanced tools such as dermoscopy or PCR-based tests may assist but are not routinely required.
Management involves eradication of mites and prevention of reinfestation. First-line therapy is permethrin 5% cream, applied to the entire body (including the scalp in children) and washed off after 8–14 hours, with a repeat application in 1–2 weeks. All close contacts must be treated simultaneously, even if asymptomatic, to prevent reinfection. Oral ivermectin is an effective alternative, especially for crusted scabies or when topical therapy fails, but is avoided in pregnancy and in small children (<15 kg). Other options include crotamiton, sulfur preparations (preferred in infants <2 months and pregnant women), and rarely lindane due to neurotoxicity risk.
Environmental control is essential: clothing, bedding, and towels used within the previous 2 days should be washed in hot water or sealed in plastic bags for at least 3 days. Household surfaces should be vacuumed. Patients should be counseled that itching may persist for 1–4 weeks after successful treatment, due to ongoing hypersensitivity, and can be managed with antihistamines or topical corticosteroids.
Complications include secondary bacterial infection, which can lead to more serious conditions such as poststreptococcal glomerulonephritis or even rheumatic heart disease in endemic areas. Treatment failure is common and usually results from incorrect application, failure to treat contacts, or missed areas (e.g., scalp, under nails). A key clinical point is to consider scabies in any patient with persistent generalized pruritus, especially if there is a history of similar symptoms in close contacts.
Scabies (Sarcoptes scabiei infestation)
Scabies is a parasitic skin infestation caused by the mite Sarcoptes scabiei var. hominis. The mites live on the skin surface, where the fertilized female burrows into the stratum corneum to lay eggs. The hallmark symptom—intense itching (pruritus)—is not due to the mites themselves but results from a delayed type IV hypersensitivity reaction to mite proteins, eggs, and fecal material. This explains why symptoms often appear 10–30 days after initial infestation, but much faster (1–3 days) with reinfestation. Although scabies has existed for thousands of years, it remains a major global health problem, particularly in crowded and resource-limited settings.
Transmission occurs mainly through prolonged skin-to-skin contact (15–20 minutes), making it common among household members, sexual partners, and institutionalized populations. Indirect spread via clothing or bedding is less common but possible because mites can survive up to 3 days off the human body. Importantly, scabies is associated more with overcrowding than poor hygiene. Most individuals harbor only 5–15 mites, but in crusted (Norwegian) scabies, seen in immunocompromised or debilitated patients, there may be thousands to millions of mites, making it highly contagious.
Clinically, patients present with generalized itching that worsens at night, often with minimal visible findings. The classic lesion is a burrow—a thin, linear, grayish track—commonly found in the finger web spaces, wrists, elbows, waistline, axillae, buttocks, and genitalia. Secondary lesions such as papules, nodules, excoriations, or superimposed bacterial infection are often more prominent than the burrows themselves. In adults, the face and scalp are usually spared, whereas infants and young children may have widespread involvement including the face, scalp, palms, and soles, often with vesicular or bullous lesions. Crusted scabies presents differently, with thick hyperkeratotic plaques, scaling, and minimal itching despite heavy infestation.
Diagnosis is primarily clinical, based on history of pruritus, typical lesion distribution, and possible contact exposure. Skin scraping of burrows examined under microscopy may reveal mites, eggs, or fecal pellets, but sensitivity is low (<50%), so a negative test does not exclude the diagnosis. In endemic settings, empiric treatment is often reasonable. Advanced tools such as dermoscopy or PCR-based tests may assist but are not routinely required.
Management involves eradication of mites and prevention of reinfestation. First-line therapy is permethrin 5% cream, applied to the entire body (including the scalp in children) and washed off after 8–14 hours, with a repeat application in 1–2 weeks. All close contacts must be treated simultaneously, even if asymptomatic, to prevent reinfection. Oral ivermectin is an effective alternative, especially for crusted scabies or when topical therapy fails, but is avoided in pregnancy and in small children (<15 kg). Other options include crotamiton, sulfur preparations (preferred in infants <2 months and pregnant women), and rarely lindane due to neurotoxicity risk.
Environmental control is essential: clothing, bedding, and towels used within the previous 2 days should be washed in hot water or sealed in plastic bags for at least 3 days. Household surfaces should be vacuumed. Patients should be counseled that itching may persist for 1–4 weeks after successful treatment, due to ongoing hypersensitivity, and can be managed with antihistamines or topical corticosteroids.
Complications include secondary bacterial infection, which can lead to more serious conditions such as poststreptococcal glomerulonephritis or even rheumatic heart disease in endemic areas. Treatment failure is common and usually results from incorrect application, failure to treat contacts, or missed areas (e.g., scalp, under nails). A key clinical point is to consider scabies in any patient with persistent generalized pruritus, especially if there is a history of similar symptoms in close contacts.
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