For microorganisms, our bodies are shelters, food and transit stations. They were not born to destroy us or make us suffer. However, natural selection tends to favor those microorganisms that are good at survival, reproduction and spreading as widely as possible, prompting them to evolve various means, and we are also implicated. For example, the plague, known as the "Black Death", has killed about 200 million people in history, and a large outbreak can wipe out the population of Europe13. Its pathogen Yersinia pestis mainly lives in mice and spreads among mice through fleas. Unfortunately, fleas still bite people, so the disaster began.

Of course, there is also an ironic fact: the physical pain caused by infectious diseases is not the purpose of pathogenic microorganisms, but the unintentional result. Some of these pains are by-products of the means taken by microorganisms to enhance their own communication ability, such as diarrhea; Some are the body's own defensive measures, such as fever (to roast microorganisms to death); Some are good for microbes and people, such as coughing and sneezing.

There will be no large-scale acute infectious diseases in primitive society-this is by no means safer. In fact, at that time, people were more likely to catch many diseases because of too much contact with animals. Only the primitive society with sparse population, scattered residence and extremely underdeveloped transportation is not enough to "feed" the epidemic of acute infectious diseases.

Agriculture enables the land to support a much larger population density than in the hunting and gathering era. Dense settlement population gives microorganisms more opportunities to spread through contact, garbage, especially water sources polluted by excreta. In an era when modern health awareness has not yet been born and the population has become dense to a certain extent, human society, especially cities, can simply be regarded as a big Petri dish for germs and a fermentation pool for infectious diseases. With enough people, pathogens can find a new group of people-the next generation-in time when all those who can be infected are infected and disappear soon.

Microorganism and evolution

In the face of foreign invaders, our bodies have a powerful chemical weapon system-immune mechanism. Immune cells patrol everywhere, searching for all suspicious foreign proteins and launching attacks. Pathogenic microorganisms have evolved deception, evasion and counterattack to fight against immunity. Then we evolved the means to deal with these means. This is a tug-of-war between you and me.

Non-fatal infectious diseases, such as leprosy, do not require high population density and may have been with us for a long time. Most of the virulent infectious diseases we are familiar with, such as smallpox and plague, are only a few thousand years old. They are the product of civilization. Large social animals may carry some pathogenic microorganisms in the wild. Our ancestors domesticated them and had close contact with them, which gave microorganisms the opportunity to adapt to the human environment and transfer between species. Cattle bring smallpox (as can be seen from the name of vaccinia vaccine), measles and tuberculosis; The flu is a gift for pigs and poultry. Of course, there are also some diseases whose origins are not animals that humans like, such as some small rodents, which approach us actively because of their rich grain reserves.

Due to genetic differences, some people are born with stronger resistance to infectious diseases and have a better chance to survive and reproduce. Therefore, the outbreak of an infectious disease will increase the proportion of people with disease-resistant genes in the post-robbery population. This is evolution. A society with a long civilization has experienced many disasters, and people's resistance to some diseases will be enhanced.

Considering the great difference between human beings and microorganisms, if human beings only passively rely on elimination and selection to carry out this endless war with microorganisms, they will always endure this cruelty. However, this is not enough. We are a special kind of creature, the first creature to actively resist natural selection. Although we kill each other in the absurd war, we are also trying to live, trying to keep the people we love alive and unwilling to be eliminated. The strangest product of evolution, the human brain, constantly seeks ways to fight diseases in pain and fear. We pray for all kinds of gods, hold strange ceremonies, treat diseases in absurd and wrong ways driven by imagination, or vent our anger on innocent scapegoats. Thousands of years after the origin of civilization, mankind finally began to correctly investigate the causes of diseases and find some really effective methods.

Microbes and public health

We tend to think of penicillin, but we also think of vaccinia and polio vaccine. Yes, the great Qinna, Pasteur, Fleming and their colleagues! In the long years, human beings are helpless in the face of invisible enemies and have been slaughtered again and again, but they don't know why. Modern medicine after the theory of bacteria finally makes it possible for us to know ourselves and ourselves. However, in addition to specific drugs and vaccines, another equally important (perhaps more important) factor in controlling infectious diseases is often forgotten by us, that is, sewers, toilets and hygiene habits. These things have penetrated deeply into our lives, and it is hard for people to feel anything special. But in fact, considering these problems, public health started in19th century.

Although archaeologists found a toilet with flushing toilet device in a Western Han Dynasty tomb in China, it was obviously not common at that time and for a long time afterwards. In Huadu Paris 16 and 17 centuries, people urinated and spilled sewage on the streets, which was not much better in other big cities (by the way, it is said that King Louis XIV only bathed twice in his life; The gorgeous wigs of the court nobles were covered with perfume and lice. Even so, the health habits of princes, nobles and civilians are not to mention. Pathogenic microorganisms are easy to survive and spread in water sources, and after floods, they are often examples of plague. Excrement pollutes public water sources, which is a key reason why serious infectious diseases are easy to spread in densely populated areas, especially in cities with poor sanitation. /kloc-In the first half of the 9th century, Edwin chadwick, an Englishman, recognized the relationship between poverty and disease when he participated in the revision of the poverty relief law, and published a book on public health in 1842. Inspired by it and troubled by the cholera epidemic in London, Britain passed the public health bill in 1848, and began to build a large-scale sewer system and set up a garbage collection system. This has greatly reduced the death rate of civilians, and other countries have followed suit. The emergence of bacterial theory provides a theoretical basis for these measures and further promotes these measures. Popularizing personal hygiene education also came into being.

Comparing SARS with infectious diseases in history, we can see that drugs and vaccines are not the only tools for us to fight infectious diseases, or even the most important tools. At the forefront of this war, the seemingly ordinary public health system, coupled with the rapid screening and isolation mechanism of cases. Yes, without a specific medicine, there will be death and sadness. However, as long as the society is still functioning normally and the public health system and the epidemic prevention and isolation mechanism have not collapsed, we can control infectious diseases in a small range, so that the hell scene of singing by thousands of families will not appear and most people will be spared the grief of losing their loved ones.