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Cholera

In August 1883, the German government sent a medical team led by Koch to Alexandria, Egypt, to investigate a cholera epidemic there. Koch soon found that the intestinal mucosa of people who died of cholera always had bacterial infection, yet could not confirm whether the bacteria were the causative pathogens. As the outbreak in Egypt declined, he was transferred to Calcutta (now Kolkata) India, where there was a more severe outbreak. He soon found that the river Ganges was the source of cholera. He performed autopsies of almost 100 bodies, and found in each bacterial infection. He identified the same bacteria from water tanks, linking the source of the infection. He isolated the bacterium in pure culture on 7 January 1884. He subsequently confirmed that the bacterium was a new species, and described as "a little bent, like a comma." His experiment using fresh blood samples indicated that the bacterium could kill red blood cells, and he hypothesized that some sort of poison was used by the bacterium to cause the disease. In 1959, Indian scientist Sambhu Nath De discovered this poison, the cholera toxin. Koch reported his discovery to the German Secretary of State for the Interior on 2 February, and published it in the Deutsche Medizinische Wochenschrift (German Medical Weekly) the following month.

Although Koch was convinced that the bacterium was the cholera pathogen, he could not entirely establish critical evidence the bacterium produced the symptoms in healthy subjects (following Koch's postulates). His experiment on animals using his pure bacteria culture did not cause the disease, and correctly explained that animals are immune to human pathogen. The bacterium was then known as "the comma bacillus", and scientifically as Bacillus comma. It was later realised that the bacterium was already described by an Italian physician Filippo Pacini in 1854, and was also observed by the Catalan physician Joaquim Balcells i Pascual around the same time. But they failed to identify the bacterium as the causative agent of cholera. Koch's colleague Richard Friedrich Johannes Pfeiffer correctly identified the comma bacillus as Pacini's vibrioni and renamed it as Vibrio cholera in 1896.