Keywords:
Scabies; Group A streptococcal pharyngitis; rheumatic heart disease; impetigo
Abstract:
Scabies is one of the world’s most prevalent diseases, with approximately 147 million cases at any one time and an estimated annual incidence of 455 million new episodes. Although Group A streptococcal (GAS) pharyngitis has long been implicated in the pathogenesis of acute rheumatic fever (ARF) and subsequent rheumatic heart disease (RHD), impetigo caused by GAS has recently been postulated as a link between scabies and the pathogenesis of ARF. In Australian Aboriginal and Torres Strait Islander populations, hereafter respectfully referred to as Indigenous, there coexists a high prevalence of impetigo, scabies and ARF whilst GAS pharyngitis is seemingly rare. The environmental and socioeconomic conditions that predispose to impetigo and scabies are also those found where ARF and RHD are frequent. Given the association of scabies with secondary impetigo often caused by GAS, and the causal role of GAS in the pathogenesis of ARF, it is possible that the skin damage caused by scabies facilitates the invasion of the skin by GAS and therefore a pathway to ARF. Molecular mechanisms that may allow scabies infection to promote GAS infection in skin lesions have been described including novel and unexpected proteins that appear important to mite survival and evasion of the host defences. The association of GAS skin infections with acute glomerulonephritis has been recognised for several decades. Two proposed mechanisms for the role of scabies in APSGN include bacterial superinfection and sepsis, and mite-mediated immune complex formation. Further research to improve our understanding of the pathogenesis of ARF/RHD and APSGN and their relationship to scabies is needed to accelerate development of more effective interventions including vaccines and to inform implementation of effective public health measures.