THE BEHAVIOR OF SARCOPTES-SCABIEI VAR HOMINIS IN HUMAN SKIN - AN ULTRASTRUCTURAL-STUDY

The biology of Sarcoptes scabiei var. hominis is poorly understood bec ause of the lack of an in vivo or in vitro propagation system. To obta in more information on the mite behaviour in its natural habitat we co nducted an ultrastructural study of burrows in a number of patients wi th common scabies. Scanning electron microscopy furnished attractive i mages of the tunnel, parasite body and eggs architecture and demonstra ted the presence of holes in the tunnel roof probably representing aer ation structures. Transmission electron microscopy showed a marked ker atinocyte damage around burrowing mites, well evident ahead of the mit e capitulum also. Faecal pellets containing keratinocyte micro-organel les (melanosomes and mitochondria) were documented in posterior midgut . For the first time we disclosed the adhesion mechanism of eggs to th e burrow floor. We showed that the typical finger-like projections of the outer layer of the egg shell gradually disappear where the eggs ar e in contact with the tunnel floor. This allows the inner layer of the egg shell to fuse and stick with the damaged keratinocytes lining the tunnel floor. Our observation substantiates that Sarcoptes scabiei pr oduces a proteolytic substance (salivary secretions?) that has a key r ole in its life cycle allowing burrowing, feeding and eggs-burrow adhe sion.