Yersinia

The genus Yersinia comprises Gram-negative rod-shaped bacteria that inhabit diverse ecosystems and includes several pathogens of humans and other animals. The most notorious species, Yersinia pestis, is the causative agent of plague, which is one of the oldest recorded infectious diseases. Plague has caused at least three major pandemics at approximately 600-year intervals starting in the 6th century AD. This pandemic began in Egypt and spread through the Middle East to Europe. The second pandemic occurred during the 14th century AD and was called The Black Death. It began in the area of the Black Sea, spread to Europe, and was responsible for the death of more than a quarter of Europe's population. The third plague pandemic, termed the Third Pandemic, began in 1855 in China and spread to India, Egypt, Portugal, Japan, Paraguay, Eastern Africa, Manila, Scotland, Australia, the United States, and several other countries. This infection is believed to have caused more than 150 epidemics of varying degrees until the 1950s. ^{1 – 3}