Chicken cholera is a highly contagious and lethal disease that occurred in epidemics in poultry yards. It is caused by the Pasteurella multocida zoonotic bacterium. It is the most common pasteurellosis of poultry. The symptoms range from acute septicaemia to chronic and localised infections - the lesions are predominantly related to vascular injuries. The morbidity and mortality may be up to 100%.
At the time of its discovery, the “germ theory” - developed in the 1800s - stated that many diseases are caused by the presence and action of specific micro-organisms. So naturally scientists were more inclined to the idea that a microbe was the cause of this debilitating disease.
The illness was one of the first infectious diseases to be recognised by Pasteur who describes the microbe as “ tiny bodies, extremely slender and constricted in the middle, which would at first sight be taken for isolated dots.”
Pasteur knew about the work done by Edward Jenner regarding smallpox and reasoned that if a vaccine could be found for smallpox, then a vaccine could be found for all diseases. Pasteur did not know how Jenner’s vaccination worked so he had to proceed searching for a chicken cholera vaccine using a process of trial and error.
Pasteur succeeded in cultivating the microbe outside the body in a neutral, sterilized broth made of ground up chicken meat. Small amounts of the broth sprinkled on the food given to chickens caused the disease and Pasteur proceeded to demonstrate that the microbe flourished in the gut of the infected chickens, and passed on the infection through the faeces. The microbe was fatal to rabbits on inoculation but when injected into the skin of guinea-pigs produced a local abscess. Such infected (but generally healthy) guinea pigs however could spread the disease to both rabbits and poultry.
In the summer of 1880, Pasteur found a vaccine by chance, after forgetting one of his cultures. With the help of a colleague Charles Chamberland, he showed that Chicken cholera germs from an old culture that had been around for some time lost their ability to transmit the disease. The inoculated chickens did not die. Pasteur repeated what he had done but with a fresh culture of chicken cholera germs. Pasteur reasoned that a new culture would provide more potent germs.
Two groups of chickens were inoculated; one that had been given the old culture and one group that had not. Those chickens that had been given the old culture survived, those that had not died. The chickens that had been inoculated with the old culture had become immune to chicken cholera. Pasteur believed that their bodies had used the weaker strain of germ to form a defence against the more powerful germs in the fresher culture.
Pasteur had found a way of producing the resistance without the risk of the disease.
- Jack Botting, ed. Regina Botting, Animals and Medicine: The Contribution of Animal Experiments to the Control of Disease. Cambridge, UK: Open Book Publishers, 2015. http://dx.doi.org/10.11647/OBP.0055
- Descour L (1922) Pasteur and his work. London: T Fisher Unwin