I very experienced allergist and friend surprised me when he treated what I thought was just a heat rash with Permethrin.  Scabies (Sarcoptes scabiei) is an itch mite that is highly contagious.  It can be sexually transmitted for sure, but it is not always so.  It does however require close contact to spread and seems limited to humans (it is not compatible with pets).  Itching is severe and it forms papules that often blister.  Microscopy scrapings can be difficult and there is even a PCR test available.