A pandemic of diseases is derived from the Greek pándēmos, with ‘pan’ referring to “all” plus ‘dêmos’ referring to "district, country, people."

Although the earliest recorded pandemic occurred in 430 B.C., Athens, the word didn’t come into being until 1666. It’s defined as a disease outbreak covering a wide geographic area (such as countries and continents), affecting a significant proportion of the population.

Three of the deadliest pandemics recorded in history were caused by a single bacterium known as Yersinia pestis, which causes plague.

The Plague of Justinian originated in 541 CE in present-day Istanbul, and spread like wildfire across Europe, Asia, North Africa and Arabia killing about 30 to 50 million people -- half of the world’s population at that time.

It returned 800 years later in Europe as the Black Death, claiming 200 million lives in four years. London experienced 40 outbreaks in about 300 years as the plague would resurface every 10 years from 1348 to 1665, killing 20 percent of the population each time.

The practice of quarantine began during the 14th century as an effort to protect coastal cities from the Black Death. The Great Plague of London led to England’s first laws to separate and isolate the sick, which eventually brought an end to the last great plague outbreak.