However, the disease caused by Y. pestis and its lifecycle is different from the other two which are quite similar. Y. pestis is the causative agent of plague, an obligate parasite of fleas and rodents where it is endemic. Transmission is from flea bite to rodent. Humans are accidental hosts. Y. pestis grows in the lymph node draining the site of innoculation causing the bubo, which is a massive inflammatory response.
Bacteria escape from the bubo and spread to other organs.
The LD 50 after subcutaneous injection in mice can be as low as 1 bacterium. Y. enterocolitica and Y. pseudotuberculosis cause enteric disease due to contaminated food or water. There is evidence that bacteria cross the intestinal barrier via the M-cell. Disease can range from mild diarrhea to what appears to be acute appendicitis to a typhoid-like septicemia. Disease occurs subsequent to invasion of the small intestine B. Similarities among the Yersiniae 1.