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.
Crusted scabies (Norwegian scabies) in a 2-year-old boy. (Used with permission from Richard P. Usatine, MD.)
The boy in Figure 128-1 with a close-up of his hand showing crusting and a fissure. (Used with permission from Richard P. Usatine, MD.)
Microscopic view of the scabies mite from a patient with crusted scabies. (Used with permission from Richard P. Usatine, MD.)
Scraping of the patient’s hand produced a good view of the scybala (the mites’ feces). (Used with permission from Richard P. Usatine, MD.)
Three hundred million cases per year are estimated worldwide.1 In some tropical countries, scabies is endemic.
The prevalence of scabies among school children in Nigeria was reported to be 4.7 percent in 2005.2
The prevalence of scabies among boarding school children in Malaysia in 2009 was found to be 8.1 percent.3
Etiology and Pathophysiology
Human scabies is caused by the mite Sarcoptes scabei, an obligate human parasite (Figure 128-3).1,4
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).
Mites move through the superficial layers of skin by secreting proteases that degrade the stratum corneum.
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