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Today, I will be talking about a deadly disease that wiped out millions of people and changed the course of human history. Yes, I am talking about the infamous disease known as the Black Death.

Yersinia pestis is a rod-shaped bacterium, measuring about 1–3 micrometres (µm) in length. It is responsible for causing three major forms of plague: bubonic plague, septicemic plague, and pneumonic plague. If bubonic plague is left untreated, the infection can spread into the bloodstream, leading to septicemic plague. It can also spread to the lungs, resulting in pneumonic plague, which is the most contagious and deadly form.

The bacterium was named after Alexandre Yersin, a bacteriologist who identified it during the Hong Kong outbreak in 1894.

The bubonic plague is the most common form of plague caused by Yersinia pestis. It is usually transmitted through the bites of infected fleas that live on rodents such as rats. In rare cases, the disease can also spread through scratches or bites from infected animals like cats or dogs, directly transmitting the bacteria to humans.

Symptoms typically appear 2–6 days after infection. Common symptoms include fever, headaches, muscle aches, weakness, and swollen lymph nodes, known as buboes. Bubonic plague does not spread directly from person to person unless it progresses into pneumonic plague, which can be transmitted through airborne droplets.

The Black Death was a devastating pandemic that occurred in the 14th century (around 1347–1351). It was primarily caused by bubonic plague but also included cases of septicemic and pneumonic plague. The pandemic killed an estimated 75–200 million people worldwide, wiping out about 30–60% of Europe’s population. The plague is believed to have originated in Central or East Asia, including parts of Mongolia and China, before spreading along trade routes to Europe.

Regions of Italy, such as Venice and Sicily, were severely affected. Due to poor sanitation, overcrowded cities, and limited medical knowledge, the disease spread rapidly. The massive loss of life led to severe economic decline, food shortages, and labor crises. During this time, doctors wore long dark robes, gloves, and beaked masks filled with herbs, believing they could protect themselves from “bad air,” also known as miasma.

Fun Fact:

The nursery rhyme “Ring Around the Rosie” is often believed to be linked to the Black Death. The “rosie” refers to the rash, “a pocket full of posies” symbolizes herbs carried to ward off bad air, and “we all fall down” represents death. However, historians still debate whether this connection is completely accurate.