A 2-year-old boy is seen with severe itching and crusting of his hands (Figures 128-1 and 128-2). He also has a pruritic rash over the rest of his body. The child has had this problem since 2 months of age and has had a number of treatments for scabies. Other adults and children in the house have itching and rash. Various attempts at treatment have only included topical preparations. A scraping was done and scabies mites and scybala (feces) were seen (Figures 128-3 and 128-4). The child and all the family members were put on ivermectin simultaneously and the Norwegian scabies cleared from the child. The family cleared as well and the child was given a repeat dose of ivermectin to avoid relapse.

Seven-year itch.

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  Three hundred million cases per year are estimated worldwide.¹ In some tropical countries, scabies is endemic.

  
  
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  The prevalence of scabies among school children in Nigeria was reported to be 4.7 percent in 2005.²

  
  
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  The prevalence of scabies among boarding school children in Malaysia in 2009 was found to be 8.1 percent.³

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  Human scabies is caused by the mite Sarcoptes scabei, an obligate human parasite (Figure 128-3).^1,4

  
  
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  Adult mites spend their entire life cycle, around 30 days, within the epidermis. After copulation the male mite dies and the female mite burrows through the superficial layers of the skin excreting feces (Figure 128-4) and laying eggs (Figure 128-5).

  
  
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  Mites move through the superficial layers of skin by secreting proteases that degrade the stratum corneum.

  
  
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  Infected individuals usually have less than 100 mites. In contrast, immunocompromised hosts can have up to 1 million mites, and are susceptible to crusted scabies also called Norwegian scabies (Figures 128-1 and 128-2, and 128-6 to 128-8).¹

  
  
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  Transmission usually occurs via direct skin contact (Figures 128-9). Scabies in adults is frequently sexually transmitted.⁵ Scabies mites can also be transmitted from animals to humans.¹

  
  
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  Mites can also survive for 3 days outside of the human epidermis allowing for infrequent transmission through bedding and clothing.

  
  
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  The incubation period is on average 3 to 4 weeks for an initial infestation. Sensitized individuals can have symptoms within hours of reexposure.

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  Scabies is more common in young children, health care workers, homeless and impoverished persons, and individuals who are immunocompromised or suffering from dementia.¹

  
  
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  Institutionalized individuals and those living in crowded conditions also have a higher incidence of the infestation.¹

Clinical Features

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  Pruritus is a hallmark of the disease.¹

  
  
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  Skin findings include papules (Figure 128-10), burrows (Figures 128-11 and 128-12) nodules (Figures 128-13), and vesiculopustules (Figure 128-14).

  
  
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  Burrows are the classic morphologic finding in scabies and the best location to find the mite (Figures 128-11 and 128-12).

  
  
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  Infants and young children can also exhibit irritability and poor feeding.

  
  
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  Pruritic papules/nodules around the axillae (Figure 128-13), umbilicus, or on the penis (Figures 128-15 and 128-16) and scrotum are highly suggestive of scabies.