Yersiniosis is a type of gastroenteritis (gastro) caused by the (germ) bacterium Yersinia. Yersiniosis can affect anyone, however, it is more common in young children. Yersiniosis occurs when Yersinia bacteria are taken in by mouth. Yersinia bacteria are found in wild, farm and pet animals and birds, particularly chickens and pigs. Y. enterocolitica belongs to a family of rod-shaped bacteria. Other species of bacteria in this family include Y. pseudotuberculosis, which causes an illness similar to Y. enterocolitica, and Y. pestis, which causes plague. Only a few strains of Y. enterocolitica cause illness in humans. The major animal reservoir for Y. enterocolitica strains that cause human illness is pigs, but other strains are also found in many other animals including rodents, rabbits, sheep, cattle, horses, dogs, and cats. In pigs, the bacteria are most likely to be found on the tonsils.