Treponema hyodysenteriae. Coloured Scanning Elect- ron Micrograph (SEM) of Treponema hyodysenteriae bacteria, cause of swine dysentery. These are Gram negative spiral-shaped bacteria of the family Spirochaetes. They cause swine dysentery by infecting the lining of the colon. Infection is found world-wide and occurs through oral contact. Symptoms include fever, diarrhoea, oedema and haemorrhage. Death occurs within days of infection due to dehydration, toxaemia or shock. This species is related to several human pathogens such as T.pallidum which causes syphilis and Leptospira interrogans, cause of Weil's disease. Magnification: x3,200 at 5x7cm size.