Crusted scabies is associated with increased IL ‐17 secretion by skin T cells

Summary Scabies is an ectoparasitic infestation by the mite Sarcoptes scabiei . Although commonly self‐limiting, a fraction of patients develop severely debilitating crusted scabies. The immune mechanisms underlying the development of crusted scabies are unclear, and undertaking longitudinal infection studies in humans is difficult. We utilized a porcine model to compare cellular immune responses in peripheral blood and skin of pigs with different clinical manifestations of scabies ( n  = 12), and in uninfected controls ( n  = 6). Although clinical symptoms were not evident until at least 4 weeks post‐infestation, the numbers of peripheral IFN γ‐secreting CD 4 + T cells and γδ T cells increased in infected pigs from week 1 post‐infestation. γδ T cells remained increased in the blood at week 15 post‐infestation. At week 15, skin cell infiltrates from pigs with crusted scabies had significantly higher CD 8 + T cell, γδ T cell and IL ‐17 + cell numbers than those with ordinary scabies. Peripheral IL ‐17 levels were not increased, suggesting that localized skin IL ‐17‐secreting T cells may play a critical role in the pathogenesis of crusted scabies development. Given the potential of anti‐ IL ‐17 immunotherapy demonstrated for other inflammatory skin diseases, this study may provide a novel therapeutic avenue for patients with recurrent crusted scabies.