The plague, best known as the Black Death that killed millions in Europe, began as a bacterial infection in wild rodent populations in Central Asia. The bacterium Yersinia pestis caused the disease. It likely first appeared in humans near the Tian Shan mountains, around what is now Kyrgyzstan, and spread along trade routes westward.
What caused the plague?
A single bacterium, Yersinia pestis, causes the plague. This germ lives in the guts of fleas that feed on rodents such as rats, marmots, and gerbils. When the flea bites an animal, the bacteria can move into the new host. If an infected flea bites a person, or if someone handles an infected animal, the bacteria can enter the human body.
The infection then travels through the lymph system and causes swollen, painful lymph nodes called buboes. That is where the name bubonic plague comes from. The bacteria can also move into the bloodstream or lungs, causing more severe forms such as septicemic or pneumonic plague.
When and where did the plague first appear?
Genetic evidence shows that Yersinia pestis evolved from a less harmful bacterium about 5,000 years ago. But the specific strain that caused the Black Death emerged much later. Research published in the journal Nature in 2015 analyzed ancient DNA from plague victims in Europe and traced the strain back to Central Asia.
A 2022 study in Nature identified the Tian Shan region in Kyrgyzstan as a likely starting point. Scientists examined DNA from teeth in graves dating to the 1330s and found the exact strain of Yersinia pestis that later reached Europe. This region sat along the Silk Road trade network, which helped the disease travel.
The plague did not begin in Europe. It arrived there in 1347, carried on ships from the Black Sea. By the time the Black Death ended around 1351, it had killed an estimated 30 to 60 percent of Europe’s population.
How did the plague spread to humans?
Plague is a zoonotic disease, meaning it jumps from animals to people. The natural cycle involves fleas and wild rodents. When rodents die from the infection, the fleas look for new hosts, including humans. Close contact with infected rats, marmots, or other small mammals can lead to bites and transmission.
People also catch plague by handling the tissue or blood of an infected animal. Hunters, trappers, and people living near rodent colonies face higher risk. In modern times, pneumonic plague can spread from person to person through droplets coughed into the air. During the Black Death, this respiratory form made the outbreak even more deadly.
How did the plague travel across continents?
Trade routes were the main highways for plague. The Silk Road connected China, Central Asia, the Middle East, and Europe. Traders, soldiers, and travelers carried infected fleas and rats in their goods, clothes, and ships. The disease moved in waves, often following busy routes of commerce and war.
The Black Death entered Europe through the port of Messina in Sicily in 1347, aboard Genoese ships returning from the Black Sea. From there it spread north and west, reaching England by 1348, Scandinavia by 1349, and Russia by 1351. The speed of travel depended on human movement — walking, riding, or sailing — not on any modern transport.
Earlier pandemics also used these routes. The Justinian Plague, which began in the 6th century, likely started in Africa or Central Asia and spread through the Roman Empire’s trade networks. That outbreak killed tens of millions before fading.
Is the plague still around today?
Yes, the plague has never disappeared. It remains present in wild rodent populations in parts of Africa, Asia, and the Americas. The United States sees about seven human cases per year, mostly in rural areas of the Southwest. Globally, the World Health Organization reports several hundred to a few thousand cases annually.
Today, plague is treatable with antibiotics if caught early. Bubonic plague has a low fatality rate with proper treatment. Pneumonic plague is more dangerous and requires immediate medical care. The risk of a large modern outbreak is very low because sanitation, public health, and rodent control are far better than in the 14th century.
Still, plague is a Category A bioterrorism agent because it can be aerosolized. Public health agencies monitor for it carefully. The bacterium that caused the great pandemics is the same one that causes infections today.
Frequently Asked Questions
Did the plague start in China?
No clear evidence proves the plague first began in China. The strongest genetic evidence points to Central Asia, near the Tian Shan mountains in modern-day Kyrgyzstan.
How long did it take for the plague to spread from Asia to Europe?
The strain that caused the Black Death likely emerged in the 1330s in Central Asia and reached Europe by 1347, a journey of roughly 10 to 15 years along trade routes.
Can you get the plague from a person’s cough?
Only if the person has pneumonic plague, which infects the lungs. This form can spread through respiratory droplets. Bubonic plague does not spread directly from person to person.
Is the plague the same as the Black Death?
The Black Death was a specific pandemic of bubonic and pneumonic plague that swept through Europe, Asia, and North Africa from 1346 to 1351. The same bacterium, Yersinia pestis, caused both.
