Why is plague so difficult to eradicate? The plague that killed hundreds of millions of people was not spread by rats

It is a great feat that humans have been able to survive and develop in such a harsh natural environment. When it comes to threats from nature, epidemics are undoubtedly one of them.

In the history of human civilization, there have been countless outbreaks of infectious diseases of different scales and types, and the one that humans are most familiar with is the plague. Plague, as the name suggests, is a disease spread by rats. Indeed, rats are carriers of the virus, but the spreaders are others.

In human history, there have been three large-scale plague outbreaks. The first occurred in the sixth century AD, during the Byzantine Empire. Because the first large-scale plague occurred too early, there are not many records of it. According to the only records that remain, we only know that the plague started in Africa and then spread to Europe and Asia, with a total death toll of more than 100 million people, but the exact number is unknown. The second plague began in the 14th century AD. This plague lasted for a long time. It is generally believed that it was not until the 17th century that the plague was truly over.

Current research believes that the second plague began in Mongolia. Because of the war, the Mongols brought the plague to the city of Kaffa. Later, the Genoese in Kaffa brought the plague to Italy and France, and then it quickly spread throughout Europe. During the first seven years of the plague, it caused the deaths of 25 million people in Europe. Later, the disease gradually spread to Asia. It is now believed that the plague pandemic in Beijing in the late Ming Dynasty in my country started with the plague that began in Europe in 1346.

Since the plague lasted for nearly 400 years worldwide, it is impossible to count how many people died, but it must have been in the hundreds of millions. On the one hand, the plague brought great disasters to mankind, but on the other hand, it also objectively promoted the development of human civilization. When the plague was rampant, no one could do anything, including the Vatican, so the authority of the Vatican was weakened, which led to the subsequent Renaissance. Because the plague caused a decrease in population, labor was scarce and labor costs increased significantly, so business owners began to try to replace manual labor with machines, which indirectly promoted the Industrial Revolution.

The raging plague also played a role in promoting the birth of science. It is now believed that the establishment of Newton's mechanics system is the symbol of the birth of modern science. Newton fled to the countryside to avoid the plague, so he was hit by an apple.

Whether this story is true or not, it is clear that the plague epidemic allowed Newton to spend more time at home to conduct his scientific research. So why was the plague so terrible and why was it so difficult to kill?

Humans really understood the plague because of the third plague pandemic. It is generally believed that the third plague pandemic began in 1850 and ended in 1950. The third plague began in Yunnan, my country. At that time, the Qing army went to Yunnan to fight and brought the plague with them. Later, the plague spread to Hong Kong through Guangdong. As an international metropolis, the outbreak of plague in Hong Kong attracted international attention, so the famous French bacteriologist Alexandre Yersin rushed to Hong Kong to study the plague. This time, Yersin finally found the bacteria that caused the plague, and humans finally understood what the plague was all about. The bacteria that caused the plague was named "Yersinia."

Yersinia is a bacterium that parasitizes mice. Mice will become sick after being infected with this bacterium, but mice cannot transmit the disease directly to humans. It needs a carrier, and this carrier is fleas.

Fleas are infected by sucking the blood of mice. Fleas infected with bacteria will feel extremely hungry due to the proliferation of bacteria in their bodies, so they will become more crazy. When they run to people to suck blood, they will also transmit this bacteria to humans. The plague that humans are infected with at this time is called "bubonic plague". Bubonic plague cannot be transmitted from person to person. If infected with bubonic plague is not effectively treated, the mortality rate is about 50%. When the condition of patients infected with bubonic plague continues to not improve, the bacteria will enter the lungs, and they will suffer from "pneumonic plague". The droplets of patients with pneumonic plague contain plague bacteria, which can be transmitted from person to person. If infected with pneumonic plague is not effectively treated, the mortality rate is 100%.

The plague bacteria not only erode the lungs, but also enter the blood. Once they enter the blood, they will cause "septicemic plague". The mortality rate of septicemic plague is 100%. Black circles will appear all over the body of the deceased, so it is also called the "Black Death."

How did the first two major outbreaks of such a terrible disease pass without modern medicine? Because plague is a disease that infects and kills very quickly, some patients will die on the same day of infection, and the longest will not exceed 10 days. Therefore, when the population density is greatly reduced due to the plague, the spread of the disease will stop. Assuming that the incubation period of plague is as long as 2 months, I am afraid that everyone will be infected in the end, and no one will be spared.

So why can't plague be completely eradicated when modern medicine is so advanced? In fact, it's not just plague. So far, the only infectious disease that has been completely eradicated by humans is smallpox. No other infectious diseases can be completely eradicated. Why? Because smallpox can only infect humans, so as long as all smallpox infected people are cured or die, then the virus will no longer exist. But this is not the case with plague and other infectious diseases. Take plague as an example. Many animals, including rats, can be infected with this bacteria. We can't eliminate all rats and animals that can be infected with this bacteria in the world, so naturally we can't completely eradicate this infectious disease.

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