Plague Spreads Like A Viral Cat Video

Plague. The Black Death. The Great Pestilence. The Great Mortality. Whatever you call it now, it was the darkest of times in the Dark Ages.

(This is part one of two about the Black Death)

You’ve definitely heard of the Great Plague. You’ve seen pictures or parodies of carts full of bodies and someone shouting, “bring out your dead!” You know it was spread by fleas on rats. But modern genetic research gives a slightly different story than the one you might have learned in Cold War-era textbooks. So, to set the record straight…

In the summer of 1346, everything seemed fine. Sure, there was the normal medieval warfare, but times were good. Trade was booming. Markets were packed. But dark shadows lurked underneath those overladen carts. Yes, it was the rats. Or more specifically, the fleas on the rats. But where did they come from?

Historians used to think that the plague came from China, but the plague actually got to China and Europe at about the same time. Blame the extremely well-connected Mongol empire, carting stuff east and west along the Silk Road. Plague originated in southwestern Russia, where Europe and Asia meet, spreading its deadly tentacles from there.

In 1346, the Mongols were laying siege to Caffa, a Genoese trading colony on the Crimean Peninsula. The Mongols got tired of the siege, so they catapulted dead bodies over the walls into the town and skedaddled. Generations of kids learned that these bodies had the plague, and that’s how it got started. But dead bodies don’t spread plague. Fleas do. And fleas love Rats. And rats love food.

So it wasn’t the war that did it. It was the peace. Trade was good. Then as now, Ukraine grew a lot of wheat, and that wheat was loaded onto boats that sailed to feed the bustling towns of the Mediterranean. Rats stowed away on wagons with the Mongols headed east to China and on boats with the Genoese headed west to Constantinople. And wherever there were rats, there were plague-infected fleas on those rats.

These fleas were infected with the Yersinia pestis bacteria. The fleas preferred rats, but once the fleas killed their rodent hosts, they would have to find a new mammal to feast upon, so they would jump to feast on humans and infect them too.

The plague came in three varieties, each more horrifying than the last: Bubonic plague, the most common (buboes included, free of charge), Pneumonic plague, which took out your respiratory system faster than you could say "achoo," and Septicemic plague, the rare but extra-deadly form that got deep in your blood.

If you had to choose which plague to catch, you want to get Bubonic plague. It had an 80% mortality rate, meaning you had a 1-in-5 chance of survival. If you got Pneumonic plague, you had only a 1% chance of survival. If you got Septicemic plague, you were gone within 24 hours. By comparison, if you got COVID in 2020-2021, your chance of survival was 98-99%. So, yeah, plague was worse.

So in 1347, plague entered Europe through the bustling port of Messina in sunny Sicily, traveling on ships loaded with grain and stowaway rats. Boats brought the rats down to Alexandria in Egypt, up the boot to the Italian republics, and all around to other Mediterranean ports. From there they rode up the rivers through France and onward to the rest of Europe. By 1348 plague had crossed the channel to England and it was game over.

The idea that one third of the population died is so old and ingrained that it’s one of those rumors that nobody knows how it got started. The numbers are much worse. In the warmer, more densely populated areas like the Mediterranean coast, it was probably more like TWO THIRDS of the population died. In more sparsely populated areas, the 1/3 death toll likely holds. So across Europe and the Middle East, more than half the population died during the peak plague years of 1347-1351.

With the population ravaged in its devastating initial wave, the pandemic started to burn itself out because there were fewer people left to infect. With entire villages emptied and the urban population decimated, the plague’s spread slowed naturally. But the Black Death didn't just fade into history after 1351, it kept coming back every generation or so, with the next plague big wave crashing in 1360. Then again in 1575, 1629, 1665, 1720 - it just kept coming back.

In the middle of the 1300s, plague went viral, even though it was caused by bacteria. So this flu season, when you’re miserable, surrounded by tissues and over-the-counter drugs, know that unlike your ancient ancestors, you will get better and live to fight another day. Use your sick days and binge your favorite shows. And if you’ve got rats, call the exterminator already. Sheesh.

Just like plague spread throughout the world in the 1300s, malware finds its way onto company systems today. The IT department is always warning the team about not clicking suspicious links, but this Nigerian prince has an offer that you just can’t refuse…

Now the whole company’s system is down and it’s all your fault. The virus you downloaded is not just in your email, it’s worming its way through the entire network, locking down files, and spreading to every connected device just like the plague at the town fair. IT is scrambling to contain the damage, but your boneheaded click has unleashed a full-scale digital disaster.

So listen to your company’s IT security teams. Don’t use the same password for everything, especially if “password” is your preferred password. Seriously, if your password is "password," it's time to rethink your approach. Delete the spam and move on. Don’t be the guy that brings a cart full of plague rats to your village.