Yersinia pestis

Yersinia pestis
A scanning electron micrograph depicting a mass of Yersinia pestis bacteria in the foregut of an infected flea
Scientific classification
Domain:	Bacteria
Phylum:	Pseudomonadota
Class:	Gammaproteobacteria
Order:	Enterobacterales
Family:	Yersiniaceae
Genus:	Yersinia
Species:	Y. pestis
Binomial name
Yersinia pestis (Lehmann & Neumann, 1896) van Loghem, 1944
Synonyms
Bacille de la peste Yersin, 1894 Bacterium pestis Lehmann & Neumann, 1896 Pasteurella pestis (Lehmann & Neumann, 1896) The Netherlands, 1920

Yersinia pestis (Y. pestis; formerly Pasteurella pestis) is a gram-negative, non-motile, coccobacillus bacterium without spores that is related to both Yersinia enterocolitica and Yersinia pseudotuberculosis, the pathogen from which Y. pestis evolved^[1][2] and responsible for the Far East scarlet-like fever. It is a facultative anaerobic organism that can infect humans via the Oriental rat flea (Xenopsylla cheopis).^[3] It causes the disease plague, which caused the Plague of Justinian and the Black Death, the deadliest pandemic in recorded history. Plague takes three main forms: pneumonic, septicemic, and bubonic. Yersinia pestis is a parasite of its host, the rat flea, which is also a parasite of rats, hence Y. pestis is a hyperparasite.

Y. pestis was discovered in 1894 by Alexandre Yersin, a Swiss/French physician and bacteriologist from the Pasteur Institute, during an epidemic of the plague in Hong Kong.^[4][5] Yersin was a member of the Pasteur school of thought. Kitasato Shibasaburō, a Japanese bacteriologist who practised Koch's methodology, was also engaged at the time in finding the causative agent of the plague.^[6] However, Yersin actually linked plague with a bacillus, initially named Pasteurella pestis; it was renamed Yersinia pestis in 1944.

Every year, between one thousand and two thousand cases of the plague are still reported to the World Health Organization.^[7] With proper antibiotic treatment, the prognosis for victims is much better than before antibiotics were developed. A five- to six-fold increase in cases occurred in Asia during the time of the Vietnam War, possibly due to the disruption of ecosystems and closer proximity between people and animals. The plague is now commonly found in sub-Saharan Africa and Madagascar, areas that now account for over 95% of reported cases. The plague also has a detrimental effect on non-human mammals;^[8] in the United States, these include the black-tailed prairie dog and the endangered black-footed ferret.