Yersinia Pestis - the Bubonic Plague Epidemic

Yersinia pestis: “The Bubonic Plague Epidemic”

The bubonic plague (also known as the “Black Death”) is one of the deadliest epidemics, eventually turning pandemic, in human history. The bubonic plague began in Europe around 1347 and lasted until 1353. The result of this epidemic killed more than 25 million people. At the time, this was more than a quarter of Europe’s population.

The pathogen causing this deadly, historic disease is known as Yersinia pestis. Y. pestis is a gram negative bacteria and a facultative anaerobe. This bacterium is bacillus shaped with unusual bi-polar staining and capsules. Its capsule and enveloped proteins protect against phagocytosis and foster intracellular growth. It belongs to the Enterobacteriaceae family, which causes most cases of severe diarrhea.

Y. pestis begins its life cycle like all bacteria. After invasion of the host, the bacterium begins the lag phase. During this phase, the bacterium has little growth. It uses this period for adjustment and enlargement. The next phase is the exponential growth phase. During this phase, maximum growth is obtained. The bacterium will remain in this stage until nutrients is no longer available. The third phase is the stationary phase. Rate of cell growth and rate of cell death becomes equal in this phase due to lack of nutrients. The last phase of the bacteria’s life cycle is the death phase. The lack of nutrients in the environment causes death of the cell.

Y. pestis enters lymph nodes of host. An incubation period of 2-6 days occurs before symptoms appear. During the incubation period, the bacterium is actively replicating. After incubation, symptoms in the host suddenly appear and the disease is now lethal. Symptoms include lack of energy, fever, headache, and chills. Swelling of lymph nodes begin to emerge, resulting from buboes. Buboes are normally found in the groin and armpit.

Y. pestis is transmitted to humans through wild animals (sylvatic plague) and domestic animals (urban plague). In most cases, a human is bite by a flea or a rodent infected with the bacteria. Y. pestis starts to multiply in infected area. The bacterium then begins to migrate to the lymph nodes of the host, and starts multiplying again. Y. pestis can also be transmitted airborne from human-to-human. This is known as pneumonic