Deadliest pandemic

The most deadly pandemic in human history was the Black Death, a pneumonic plague pandemic that spread across Europe, Asia and North Africa between 1346 and 1353. The death toll of this disease is impossible to know exactly, but credible estimates range from 25 million to 200 million (with most estimates falling in the 50–100 million range). For context, at the time the total global population was likely not much more than 400 million.

The bacterium that causes the plague, Yersinia pestis, is named after the French scientist that discovered it in 1894, Alexandre Yersin. This bacterium is transmitted by fleas that live on rodents. When rodents die of plague, the fleas jump to a new host and transmits the plague to them.

The most common form of plague was Bubonic plague, which caused painful buboes, or swellings, on the victims. These turned black, leading to the name ‘Black Death’. The pneumonic plague is much more infectious, and affects victims’ lungs.

The arrival of a new and dangerous strain of plague in the 16th century caused a second wave of this pandemic, and the most recent plague pandemic spread across Asia in the late 19th century.