Plague, the bacterium Yersinia pestis,China

Plague, the bacterium Yersinia pestis,China

 

'Plague' is the name given to any disease caused by the bacterium Yersinia pestis. Plague is considered one of the few history-changing diseases, killing hundreds of millions of people in the last 1,500 years.

The first major pandemic occurred in the 6th century AD. It began in Africa and spread to the entire Mediterranean basin. Estimates of this pandemic alone put the death toll at about 100 million, helping to contribute to the fall of the Roman Empire. In the 1300s, the more infamous 'Great Plague,' also known as the 'Black Death' pandemic, started in China, eventually reaching Europe. Over the next several hundred years, plague decimated the population of Europe, killing between 25-33% of the population of the continent with every new outbreak.

Some outbreaks claimed upwards of 60 million lives, leaving too few healthy laborers to even bury the dead, let alone providing for daily needs of the survivors. The last great pandemic started in the late 1800s, spreading from Asia in rat-infested ships. By 1900, some of those rats had reached San Francisco, depositing Yersinia pestis in the New World.

Once in the United States, Yersinia pestis found a new host: the prairie dog. These rodents, in addition to chipmunks, squirrels, and the usual rats and mice, have maintained plague in the United States to this day. Fortunately, not many people are ever directly in contact with these rodents, so actual cases of plague are rare. The U.S. averages around 10 cases of plague every year.

In developed countries, plague is a rarity, but cases have been rising recently in less-developed countries. Overcrowding and poor sanitation has led to an increase in rat populations. More rats means more fleas, which means more vectors for Yersinia infection.