Most people think they know the answer to when did bubonic plague start. You probably picture a filthy medieval street in 1347. Rats scurrying underfoot. People wearing those creepy bird-shaped masks. While the "Black Death" of the 14th century is the one that gets all the movies and history books, it wasn't the beginning. Not by a long shot. Honestly, the plague is way older than our recorded history of it, and it has been tagging along with humanity since we were basically living in huts and just starting to trade across borders.
If we're talking about the very first time Yersinia pestis—the actual bacteria—showed up in humans, we have to look back nearly 5,000 years. This isn't just a guess. Scientists like Eske Willerslev and Simon Rasmussen have literally pulled plague DNA out of Bronze Age skeletons. So, if you're looking for a hard date for when the plague began its relationship with us, you’re looking at roughly 3000 BCE.
But back then, it was different. It didn't have the "fleaborne" upgrade yet. It couldn't cause that horrific swelling in the lymph nodes we call buboes. It was just a weird, deadly blood infection.
The First Big One: The Plague of Justinian
Before the famous medieval outbreak, there was the First Pandemic. It hit in 541 CE. At the time, the Byzantine Empire was trying to put the Roman Empire back together. Justinian I was the Emperor, and things were actually looking up for him until the grain ships arrived in Egypt.
Those ships weren't just carrying food. They were carrying the end of an era.
This outbreak is the first massive, documented instance of what we’d call a "bubonic" plague. It killed millions. Some estimates say 25% to 50% of the population in the Mediterranean world just vanished. Imagine waking up and half your neighborhood is gone in a week. It’s hard to wrap your head around. Procopius, a historian from that time, wrote about people hallucinating and falling into sudden fevers. He basically thought the world was ending.
Eventually, it fizzled out, but it didn't disappear. It just went into hiding. It lingered in rodent populations, waiting for the right climate conditions to jump back into humans. This is a pattern we see over and over again. The plague isn't a one-and-done event; it's a recurring character in human history.
Why 1347 Is the Date Everyone Remembers
So, if it started in the Bronze Age and blew up in 541, why does everyone point to 1347?
Because that’s when the "Black Death" hit Europe. This is the Second Pandemic. It’s the big one. It changed everything—from how much peasants got paid to the way people viewed the Church.
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It started in Central Asia. Geneticists have traced the specific strain to the Tian Shan mountains. From there, it hitched a ride on the Silk Road. It reached the Crimea, specifically a trading port called Caffa. There’s a famous (and probably slightly exaggerated) story that the Mongols threw plague-infested corpses over the city walls using catapults.
Whether that’s 100% true or not, the result was the same. Italian merchants fled Caffa on ships. When they docked in Sicily, they were carrying a death sentence.
- By 1348, it was in Paris.
- By 1349, it had reached London.
- By 1350, it was clearing out villages in Scandinavia.
It was fast. It was brutal. It was terrifying because nobody knew what was happening. They thought it was "miasma" or bad air. They thought it was a punishment from God. They had no idea that a tiny bacterium was hitching a ride on a flea, which was hitching a ride on a rat, which was hitching a ride on their own clothes.
The Biological Evolution of the Plague
To understand when did bubonic plague start, you have to understand how it evolved. Yersinia pestis is a descendant of a much milder bacterium called Yersinia pseudotuberculosis. That older version just gave you an upset stomach.
Around 3,000 to 4,000 years ago, it picked up a specific gene called ymt. This tiny bit of genetic code allowed the bacteria to survive inside a flea's gut. Before that, a flea would bite you, and nothing would happen. After that? The flea became a biological syringe.
This evolution is why the plague became so much more dangerous during the Middle Ages compared to the Bronze Age. It wasn't just a disease you caught from dirty water or coughing; it was a disease that lived on the very animals that lived in your house.
Misconceptions About the "Start" of the Plague
People often get confused about the different types of plague. It’s all the same bacteria, but how you get it determines what it’s called.
- Bubonic: The flea bites you. Your lymph nodes swell up into "buboes." This is the most common version.
- Septicemic: The bacteria gets straight into your blood. You turn black (necrosis) and die very fast.
- Pneumonic: This is the scary one. It’s in the lungs. You cough it out. Now it's airborne. You don't need a rat or a flea anymore. You just need to breathe.
When people ask when the plague started, they usually mean the bubonic form. But the pneumonic version is likely what made the Black Death move so incredibly fast across Europe. It didn't wait for the rats to catch up.
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The Third Pandemic: The One You Didn't Know About
You’d think after the Middle Ages, we’d be done. Nope.
The Third Pandemic started in the mid-19th century. It began in the Yunnan province of China in 1855. It eventually hit Hong Kong and then spread to the rest of the world via steamships. This is actually the pandemic that allowed us to finally understand the disease.
In 1894, a physician named Alexandre Yersin finally isolated the bacteria (hence the name Yersinia). He realized it wasn't bad air. It was a germ. Shortly after, Paul-Louis Simond figured out the flea connection. It only took us about 4,500 years to figure out what was killing us.
This third wave hit places the plague had never really been before, like San Francisco and Australia. It lingered in the United States, which is why we still have plague cases today in the Southwest. If you see a sign in a California park telling you not to feed the ground squirrels because of the plague, you can thank the Third Pandemic for that.
Is the Plague Still Starting Today?
Technically, the plague hasn't ended. It’s just managed.
Every year, there are roughly 300 to 600 cases reported worldwide. Most of these are in Madagascar, the Democratic Republic of the Congo, and Peru. In the U.S., we usually see about seven cases a year. It’s not a death sentence anymore because we have antibiotics like streptomycin and gentamicin. If you catch it early, you're fine.
But there’s a catch.
Scientists are worried about antibiotic resistance. In Madagascar, they found a strain that was resistant to multiple drugs. If that strain starts to spread, we might find ourselves asking "when did the next plague start" sooner than we’d like.
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Why History Matters for Your Health
Knowing the timeline of the plague isn't just for trivia night. It shows us how diseases jump from animals to humans—a process called zoonosis. This is the same way we got COVID-19, Ebola, and the Bird Flu.
The plague started when humans began living in closer proximity to animals and each other. It flourished when trade routes expanded. It moved faster when our transportation got better. The history of the plague is really just the history of human globalization.
Actionable Steps for the Modern World
While you don't need to walk around in a leather mask, there are real things to keep in mind regarding the plague today.
1. Watch the rodents.
If you live in the Western U.S. or other endemic areas, stay away from wild rodents. Prairie dogs, ground squirrels, and chipmunks carry the fleas that carry the plague. If you see a bunch of dead squirrels in one area, don't touch them. Call local wildlife authorities.
2. Protect your pets.
Cats are extremely susceptible to the plague. They can catch it from hunting infected rodents and then bring the fleas (or the disease itself) to you. Use flea prevention religiously if your pets go outside in high-risk areas.
3. Recognize the symptoms.
It starts like the flu. Fever, headache, chills. But if it’s bubonic, you’ll get those tell-tale swollen, painful lymph nodes (buboes) in the groin, armpit, or neck. Early treatment is the difference between a week in the hospital and a permanent spot in a cemetery.
4. Stay informed on "One Health."
Support initiatives that monitor animal health. By tracking the plague in rodent populations now, scientists can predict and prevent human outbreaks before they start.
The story of when the bubonic plague started is a long, messy timeline of evolution and human movement. It didn't start in 1347; it started the moment we began reshaping the world to fit our needs, creating a perfect environment for a tiny bacterium to thrive. We’ve lived with it for 5,000 years. With proper science and caution, we can make sure the next big chapter in its history never gets written.