Scanning electron microscopy of the lesions of swine dysentery.

Thirty weanling pigs were examined by scanning electron microscopy at various time intervals after oral inoculation with crude colon contents from pigs affected with dysentery. The earliest recognizable change was a corrugated appearance of the mucosal surface of the large intestine. Large spirochetes, morphologically similar to Treponema hyodysenteriae, were first observed within the crypts of Lieberkühn where they seemed to proliferate onto the luminal surface. Then mucus, fibrin, erythrocytes, and disrupted epithelium appeared. Large spirochetes were always abundant in those lesions, but variable numbers of other mixed bacterial forms were also present. The earliest changes could be correlated with the appearance of large spirochetes in the feces and with early clinical signs, but not with a specific postinoculation time. Once bloody diarrhea was present, no consistent pattern was observed in development, location, or form of the lesions. With time, the lesions merely came to involve an increasingly greater surface area of the large intestine.