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If each new case causes an average of more than one person with subsequent infections (ie, R0> 1) , the epidemic is likely to spread ; If each new case results in an average of less than one person’s subsequent infection (ie, R0 <1) , the epidemic will gradually disappear.

The value of R0 is one of the most important indicators for measuring the spread of the epidemic.

In epidemiology, whether a microorganism that is spreading is identified as an “epidemic” has nothing to do with its lethality, it has nothing to do with its infectivity, that is to say with the value of this R0. An epidemic may “viral spread” or disappear gradually, depending on this R0.

So, the “inflection point” of the epidemic situation is actually the point at which the value of R0 drops. The trend of the epidemic situation has changed, the average number of infected people per case is very small,Will slowly disappear.

(Schematic diagram of the R0 values ​​of several viruses and their infectivity: from top to bottom, left to right, Zika virus, measles Virus, Ebola virus, HIV, Chikungunya virus, seasonal flu and Norovirus)

“Knee”, what is it after turning?

After talking about the “inflection point”, let’s talk about the relationship between a virus “infectiousness” and “inflection point”. Isn’t the more infectious virus more terrible? The more contagious the “inflection point”, the less likely it is to arrive?

The answer is a bit counterintuitive: No .

Let’s imagine that a highly infectious virus like New Coronary Pneumonia virus or SARS virus will spread quickly in the crowd, kill some people quickly, and quickly make the remaining people develop antibodies.

However, after a period of transmission, because the total population is limited, the proportion of the population that has not been exposed to the virus begins to decline. That said, most people soon became infected.

So, the “infection rate” of the virus will definitely be lower than the “recovery rate” of people recovering from the infection. Once this happens, the number of infected people must continue to decline, and the “inflection point” will almost come. After that, even without medical intervention, the epidemic will eventually weaken.

In other words, The more contagious the epidemic, the shorter the duration and the earlier the inflection point will come . Statistically, highly infectious viruses like SARS and Ebola follow this pattern.

(During the Ebola outbreak, the relationship between the number of people infected and the time (week))

Conversely, some very infectious viruses are even more terrible.

For example, the “ Human Immunodeficiency Virus “, which causes AIDS, is very infectious. Even if we are in close contact with an infected person, we will not be infected as long as there is no fluid exchange.

But this means that the majority of people who are not infected with AIDS will always be the majority. Even after decades, the number of infected people continues to increase, and that “inflection point” cannot arrive late.

In 2019 alone, there were 37.9 million people living with HIV worldwide, and about 958,000 people living with HIV in China.

In addition, there is another important point: Even if the “inflection point” comes, even if the epidemic has completely passed, there is no guarantee that it will not make a comeback, because the virus is difficult to eliminate.

Variola virus is a prime example.

In 1979, humans claimed to have eliminated variola virus from the earth. This is true, but it was only eliminated in humans. The primates (that is, ape species) still have “relatives” of variola virus, such as “Monkey smallpox virus” in monkeys.

(Certificate of the Global Confirmation Committee on the Fight against Smallpox, written in 6 languages: Humans have eliminated smallpox virus)

With the disappearance of the smallpox virus, the smallpox vaccine has stopped, and more and more children without variola antibodies are born, so people are more likely to be infected with smallpox virus, which will bury the smallpox that may break out at any time. Hidden danger.

In 2007, “Monkey Smallpox” broke out in the Democratic Republic of Congo in Africa, and more than 500 people were infected with systemic pustules and severe rashes. Ten years later, in 2017, a large-scale outbreak occurred in Nigeria, Africa. “Monkeypox” virus, this is the first case of monkeypox in the country in 40 years; in 2018, “monkeypox” also appeared in Western Europe, and many people were infected.

“Smallpox” seems to be back, and it is a virus that has been “extinct” by us. So what about those viruses that didn’t go extinct?

For example, although SARS has disappeared for many years, the degree of threat they pose to us today may be the same as when they were first noticed;

Another example is the “new crown virus”. When it finally “disappears”, it will just be hidden. I don’t know when it will appear next time.

An inflection point for an epidemic will come sooner or later, but the grand historical inflection point for humans to fight the epidemic will not come so easily. Looking into the future, this is the problem we need to solve.

But before we look to the future, let’s go back to the past.

From a viral perspective, which three “big inflection points” have human society experienced?

Why is our human society so vulnerable to a pandemic? Because from a viral perspective, the development of our human society,Going through three important “inflection points”.

The three “inflection points” are: Hunting and slaughter, domestication revolution, and modern life .

The first “inflection point”: hunting and killing activities

This “inflection point” appeared 8 million years ago.

The author has carefully observed chimpanzees in African jungles, hunting and eating red colobus monkeys on trees. You may not know that chimps really love monkey meat.

The body of the chimpanzee may be bruised during the hunting process; during the monkey eating process, the blood, saliva, and feces of the monkey splashed into the chimpanzee’s body opening “label =” Remarks “> (eyes, nose, mouth, wounds on the body) . The process of hunting and eating red colobus monkeys by chimpanzees has spread all the infection sources on the monkeys to the chimpanzees.

8 million years ago, our ancestors started hunting various animals just like today’s chimpanzees. This “dirty and messy” behavior of hunting activities provides all the conditions for the virus to spread between species. Since then, the way we interact with microbes has changed forever.

Let’s compare hunting with mosquito bites.

Everyone knows that mosquitoes can also spread diseases. However, the mosquito must first suck the blood of an animal into its stomach. Subsequently, the mosquito’s stomach will kill a considerable part of them.Then, the mosquito sucks the blood of the second animal. In the process, the mosquito spit out water, and the saliva contained the microorganisms that had not been killed. In this way, the second animal becomes infected.

In contrast, the hunting and slaughtering activities brought the blood, saliva, and feces of the two animals into direct contact, and instantly completed the tasks that the mosquitoes could twist and turn.

Therefore, hunting and slaughtering is a viral “highway” compared to the “sheep intestine trail” built by mosquitoes. It keeps viruses coming and going between individuals and species, constantly amplifying their ability to spread.

The author also said vividly: “Hunting” is sex in the eyes of viruses, and “slaughter” is the orgasm in the eyes of viruses; at those moments when blood is shining, passionate viruses are all excited.

The second “inflection point”: the domestication revolution

This “inflection point” appeared 10,000 to 12,000 years ago.

10,000 to 12 thousand years ago, humans began to domesticate sheep and grow rye. Starting from this, domestication and reproduction of various plants and animals have subsequently emerged, which we can call: domestication revolution (domestication revolution ) .

5,000 to 10,000 years ago, human domestication reached its peak. Since then, human beings can have a fixed source of food all year round, and do not need to chase around the rhythm of nature. However, this also brings three incidental issues:

First, this promotes the spread of microorganisms from livestock to humans.

Microbes from livestock spread to humans, and are constantly changing.Writes human history.

In the book Guns, Bacteria, and Steel, Jared Diamond argues that there are more livestock in temperate regions, and there are more microorganisms and rich diversity in temperate populations.

In contrast, Native Americans lacked the experience of raising domestic animals. Their bodies encountered fewer germs, and they were completely immune to some germs.

So, in the 16th century, Indians and Spanish in Mexico immediately fell into disuse. At that time, Mexico’s population plummeted from 20 million to 1.6 million, and 95% of Indians died of smallpox, measles and flu brought by Europeans.

Recalling that period of history, Jared Diamond said: “The victors of the past wars were not always those with the best generals and the best weapons, but often those who carried contagious The enemy’s dirtiest germ. “

Secondly, domestication has provided a large-scale community for human beings, which has become a breeding ground for microorganisms.

Remember what you said just now, the more contagious the epidemic, the shorter the duration, the sooner the inflection point comes. If humans live in a small community with a relatively small number, then a very contagious epidemic will soon infect most people in this community.

When the dead have died, the survivors are individuals who can resist the disease. In this way, the epidemic will end naturally. Therefore, in such a small community, many diseases cannot be epidemic; many microbial outbreaks can only be a “flash in the pan” state.

(herdsmen and livestock in Tassili-n-Ajjer petroglyphs, Algeria)

Conversely, if humans live in large-scale communities with a large number of people, then an epidemic situation can be transmitted from person to person for a long time, and the “inflection point” will be delayed, resulting in mass infection, Scale spread.

Furthermore, most of the animals that grow on large farms will not be in good isolation. Contact with bloodthirsty insects, rodents, birds and bats will enter these huge animals for new sources of infection. Community, providing opportunities.

At this time, some microbes that were only transient can now survive in large communities. They stayed around our species and became “time bombs.”

Finally, a large number of domestic animals were reared intensively, and new types of microorganisms were cultivated.

When microbes that were supposed to be “a flash in the pan” survived, we gave them a chance to mutate.

If you stick to it for a day, they will have a day to mutate into a new and more terrible disease-more suitable for the human body, and more suitable for spreading from person to person.

For example, “avian influenza virus”, when it is uploaded from birds to humans, it may be mutated due to selection pressure. After the mutation, the human body’s original antibodies lose their effect, and a new wave of “avian flu” can re-emerge. This cycle can be repeated many times.

The third” inflection point “: modern life

This “inflection point” appeared around the 20th century.

A major feature of modern life is the well-developed transportation, which increases the “mobility” of the population, which in turn promotes the spread of infectious diseases.

Two experts at Harvard University have analyzed the flu outbreak in the United States from 1996 to 2005 and air travel in the United States. By comparison, they found that, based on the number of U.S. air travellers, the speed of transmission of the flu in the United States can be basically predicted.

For example, in 2001, a travel ban occurred after the “911” incident, because the population movement caused by aviation was affected, and the flu season that year was delayed accordingly.

In addition to “mobility”, there are other characteristics of modern life, such as urbanization, high population concentration, deforestation and game consumption. These multiple factors “collusion” create conditions for the emergence of diseases, This created the third “inflection point” between human and microbiological relationships.

In the future, where is the real “inflection point”?

So, where is the next important “inflection point”?

The spread of AIDS globally is a lesson. It can be said that humans have basically failed in the fight against AIDS. In other words, the traditional process of onset, spread, isolation, and treatment no longer works.

So we need a new idea: The main work in the future against epidemics is not “governance” but “prevention”.

This “prevention” includes not only preventing the spread of epidemics, but also predicting the occurrence of epidemics. We need to use sufficient data and information to detect possible spread epidemics as early as possible in the new microbial pandemicPreviously, they were “captured in place” to avoid spreading to more areas.

The author believes that there are three specific methods.

Monitor high-incidence crowds early

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Many new viruses and epidemics are hidden near some remote villages in the world, but they are not known to the outside world because of inconvenient transportation and poor information. But it is these places that deserve our close attention.

In these remote villages, some of them are “ Sentinel Crowds “. What does that mean? Those who are in frequent contact with wild animals have a higher infection rate than others.

The sentinel crowds are often hunters, people engaged in hunting activities, and they are always at the “front line” of the virus from animals to humans. Monitoring them is something we must always do in the future.

The author has set up some rural monitoring points in Central Africa to collect microbial samples, store them carefully, and then transport them out through complicated international agreements for laboratory research.

In this way, the author and other experts discovered a “ monkey foam virus “, and the virus has begun to spread to locals. It is worth noting that there was no foam virus in humans before, and no public health agency knew about it.

So, In the future, we need to expand this “monitoring point” and turn it into a “monitoring network” To establish a global control system, monitor those who are most in contact with wildlife, monitor and study the microbial conditions on them, and strive to achieve these three points:

1. Early identification of endemic diseases;

2. Assess the probability of an endemic epidemic becoming a global epidemic;

3. Stop deadly endemic epidemics before they become global epidemics.

Take a new monitoring hand

This depends on the power of technology. For example, Google experts have developed a system that defeats traditional American disease surveillance systems.

What happened? The idea of ​​the Google team is that after people are exposed to infectious diseases, the pattern of online searches may change. As a result, Google’s research team has built a system that predicts flu trends by tracking the words people search for-words related to flu symptoms and treatments, for example.

Comparatively, the traditional surveillance system of the US Centers for Disease Control and Prevention requires a certain period of time to collect, publish and report data. Therefore, the comparison found that the system developed by Google is more accurate than the flu statistics provided by the US Centers for Disease Control and Prevention.