False colour transmission electron micrograph of the bacterium Leptospira sp., which occurs as a long thin spiral (20x0.1 micrometres in size). The bacterium is coloured red. Leptospira is one of a group of helical bacteria called spirochaetes, which contains many serious pathogens. The parasitic species L. icterohaemorrhagiae causes leptospirosis, known as Weill's disease, which affects the liver (jaundice) or the meninges of the brain (meningitis). Infection is through contact with rodents, dogs & farm animals: farmers, sewage workers & veterinary surgeons are susceptible to the organism. Treatment is with penicillin. Magnification: x4,400 at 35mm size.