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 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.