A study of the pathogenesis of local skin necrosis induced by Naja nigricollis (spitting cobra) venom using simple histological staining techniques.

The course of degeneration and regeneration of mouse skin following intradermal injection of spitting cobra (N. nigricollis) venom was investigated using simple histological staining techniques. Early changes observed were vascular congestion, oedema and degeneration of the skeletal muscle cell layer (panniculus carnosus) in the area local to the injection site. Fuchsin staining of degenerative muscle cells in haematoxylin-basic fuchsin-picric acid (HBFP) stained sections appeared long before any detectable change was obvious in serial sections stained with haematoxylin and eosin (H and E). Positive reactions were apparent as early as 5 min after venom injection. Infiltration by a mixed population of cells was observed 1 hr after injection. Twenty four hours after injection large numbers of neutrophils, eosinophils, macrophages and mast cells were observed in and around the necrotic tissue and there was evidence of fibrin deposition in the blood vessels. A newly formed epithelium and muscle cell layer was visible after 18 days. The destroyed tissue tended to slough, leaving behind granular scar tissue. Dense granular scar tissue had generally replaced the damaged tissue after 28 days. It appears likely that myonecrosis was due to the direct myolytic action of one or more venom components, since signs of damage were apparent as early as 5 min after injection. However, the venom also caused fibrin deposition, suggesting possible thrombus formation later, and so it is also probable that some contribution to the degenerative state may be attributable to ischaemia brought about by a diminished blood supply.