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[peterescue]

Its bacterial. IIt can be caused by keeping in por hygenieic conditions or other factors that cause your reptile to lose condition. Poor general health and stress can also contribute. A small lesion on a snake in poor condition can lead to scale rot or canker.
Betadine solution(povodine iodine) or Chlorhexadine(chlorex)solution(2%) and what jonno said.

ps. remove any dead skin or flesh and dress the wound using a topical antiseptic paste and "opsite" or similar. Betadine cream is ok but Silvazine if you can get some.
We been finding better results with dressing wounds. They heal much faster.