The plague known over the years as the Black Death, Black Plague, and the Great Plague is an infectious disease caused by the bacterium Yersinia pestis. Yersinia pestis was formerly known as Pasteurella pestis but its name was changed in the year of 1944. This bacteria is primarily found in tiny mammals and the fleas that live on said mammals. The fleas that become infected with the Y. pestis bacterium has a biofilm mass from said bacteria blocking the foregut of the flea. Since the foregut is blocked, the Y. pestis bacteria is regurgitated into the wound of the uninfected host and causes the plague infection. This bacterium causes the plague and can take three main forms. These are known as the bubonic, pneumonic, and septicemic plague. The three of these were responsible for huge epidemics and a very high-mortality rate that devastated human history. The plague has an extraordinary place in history and also had serious implications on the progress of modern civilizations as a whole. During the worst plague and epidemic recorded in human history, the population dropped from 450 million people to 350 million. That means 100 million people perished due to this bacteria. All three forms of the plague can become fatal if they are not promptly treated and looked after. Globally, up to 1,000 – 3,000 cases of the plague are reported each and every year. The beginning symptoms are flu like and indistinguishable. But as the bacteria and disease advance on, the bubonic plague infects and makes the lymph nodes swell. The most life threatening but rare plague is the pneumonic, it can be transmitted via human to human through the pulmonary system and essentially blocks the airways.
Yersinia pestis is coccobacillus, gram-negative, rod shaped non-motile, zoonotic bacteria that is sporeless. It is also positive in catalase but negative in oxidase, urease, and indole. The bacteria likes rodents, fleas, and humans and prefers the human body temperature of 37°C. Rather than the virulence factors being encoded by the bacterial DNA, it is encoded by the bacterial plasmids. This as well as the hemin storage system locus (hms) contributes to the pathogenicity of this bacteria in fleas.