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Yersinia

There are different types of Yersinia, which are bacteria that can grow with or without oxygen. Yersinia pestis are the bacteria that cause plague. Approximately 1 to 3 percent of diarrhea illnesses are caused by Yersinia enterocolitica. Yersinia pseudotuberculosis is the closest genetic relative to Yersinia pestis, but can be distinguished from it by the symptoms it causes and by laboratory test results.
 

Yersinia: An Introduction

Yersinia are Gram-negative bacteria that can grow with or without oxygen (a quality called facultative anaerobic). Although there are 11 named species in the genus Yersinia, only three are considered important human pathogens:
 
Yersinia bacteria were formerly classified in the Pasteurellaceae family, but, based on their similarities to Escherichia coli (E. coli), the Yersinia group has been reclassified as members of the Enterobacteriaceae family.
 

Yersinia Pestis

Yersinia pestis are the bacteria that cause plague. They are found in rodents and their fleas, and occur in many areas of the world, including the United States. Other animals can carry Yersinia pestis. Rock squirrels and their fleas are the most frequent sources of human infection in the Southwestern United States. As for the Pacific states, the California ground squirrel and its fleas are the most common source.
 
Yersinia pestis transmission from infected animals generally occurs in one of three ways:
 
  • Bites from infected rodent fleas (about 85 percent of cases)
  • Direct contact with infected tissue or bodily fluids
  • Inhaling infected droplets.
     
(Click Plague Transmission for more information on how plague bacteria are transmitted.)
 
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Written by/reviewed by: Arthur Schoenstadt, MD
Last reviewed by: Arthur Schoenstadt, MD