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After a distressing episode involving my elderly mother and a nursing home, I've been reading up on scabies. It seems that in healthy people, the immune system limits the mite population to around 10 of the creatures at any one time; elderly and immunocompromised people can be infested by many more - thousands, even millions of mites (shudder).

So my question is, given that the mites burrow in the top, dead, layer of the skin, how does the immune system detect them and suppress them at all? Conversely, if the immune system can limit the mite population so effectively, why doesn't it wipe them out entirely?

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    $\begingroup$ Welcome to Biology.SE! I think this is a very good question and made some edits to clarify it. Please feel free to further edit! $\endgroup$ – AlexDeLarge May 12 '17 at 11:17
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    $\begingroup$ @Alex Thanks. I have only reverted the 'S' in the question, b/c I believe 'scabies' isn't a plural - same as eg 'measles' $\endgroup$ – peterG May 12 '17 at 13:02
  • $\begingroup$ Did you do any reaearch, say, into the immunology of susceptibility and resistance to scabies? If so, what did you find? On this site, some attempt to answer the question, even if the research doesn't help, is expected and appreciated. (Btw, I never heard that number. And from the numbers of healthy people I've had to treat for scabies - and having suffered a bad infection myself in early adolescence [an unforgettible experience] - I'd say the immune system is not all that great at suppressing the infection.) $\endgroup$ – anongoodnurse May 12 '17 at 18:12
  • $\begingroup$ @anongoodnurse As in my OP, my research consisted of googling 'scabies', the results of which led me to those figures. (eg Wikipedia suggests a number as high as 2 million mites for encrusted scabies.) I don't really have access to anything more specialised, which is why I posed the question on here. $\endgroup$ – peterG May 12 '17 at 19:13
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Found from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3535073/

"In addition to being a physical barrier, the skin is an immunological barrier63. The skin immune response is vital in wounding and infection and also modulates the commensal microbiota that colonizes the skin. Keratinocytes continuously sample the microbiota colonizing the skin surface through pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs), mannose receptors and the NOD-like receptors. These receptors recognize pathogen-associated molecular patterns (PAMPs) including flagellin and nucleic acids, as well as lipopolysaccharide from Gram-negative bacteria, mannan and zymosin from fungal cell walls, and peptidoglycan and lipoteichoic acid from Gram-positive bacteria. The activation of keratinocyte PRRs by PAMPs immediately initiates the innate immune response, resulting in the secretion of antimicrobial peptides (AMPs), cytokines and chemokines. Beyond effecting an adaptive immune response, AMPs also directly kill bacteria, fungi and enveloped viruses64. Therefore, there is a constant interplay among keratinocytes, immune cells and microorganisms that is modulated by AMPs, cytokines, chemokines and microbial peptides."

While mites certainly are not fungal, viral, or bacterial, you can extrapolate the mechanisms required to prevent mite infestation being similar to those referenced above. Hope this helps!

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protected by Chris Jan 12 at 21:17

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