Infectious contagion: why the coronavirus will not turn into a global threat (UPD.)

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Infectious contagion: why the coronavirus will not turn into a global threat (UPD.)
Infectious contagion: why the coronavirus will not turn into a global threat (UPD.)
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Recent scientific work predicted a serious 2019-nCoV coronavirus epidemic. According to her, 95% of those infected have not yet been registered by the authorities, which means that in a couple of weeks there will be hundreds of thousands of cases in Wuhan alone. With an observed mortality rate from the virus of 2.36%, this is many thousands of deaths. In fact, the new work is more likely to "catch the hype" or, if you like, tries to keep the world on guard, than describes a real epidemic. The latest data on the contagiousness of the coronavirus show that it is indeed not brilliantly transmitted from person to person. This is enough for an epidemic in China, but a large number of victims outside this country is unlikely. Find out why.

2019-nCoV continues to spread actively and has every chance to outshine the SARS epidemic of 18 years ago / © discovervirus.com

UPD. The article continues.

A group of researchers led by Jonathan Reed from Lancaster University tried to predict the extent of the ongoing 2019 coronavirus epidemic. In an article posted on the server of scientific papers medRxiv, they calculated that by January 21, there were 11 thousand infected, and by February 4 there will be almost 200 thousand.

To date, mortality from the new virus 2, 37% - 107 out of 4515 cases. If the authors of the new work were right, Wuhan alone is doomed to lose many thousands of lives only in the coming February.

Contagiousness Index: fairly moderate

Most of the papers on medRxiv are labeled as "not peer-reviewed." The new one is from this number. Consequently, the obvious mistakes of the authors there may not be caught by the reviewers. A scientific review takes a long time, but to understand whether the authors are right or not, you can already today.

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The key parameter of any epidemic is the basic indicator of the reproduction of the infection. It is equal to the number of people that the average carrier of the infection can infect. Any model of the spread of epidemics calculates this indicator: and the higher it is, the more infectious the disease and the more powerful the epidemic.

The record holder here is common measles. In an unvaccinated (and not sick with measles in childhood) population, one patient infects an average of 15 people with it. Such an infection is extremely dangerous even with a low mortality rate: in a society without a vaccine, almost everyone was sick with measles, exceptions are extremely rare. Even with a death rate of 0.1% globally, many millions would die from such a disease.

In the new work, the number 3, 8 (the average number of the interval 3, 6-4, 0) was taken as the baseline reproduction rate for the 2019-nCoV coronavirus: 10 cases will transmit the disease to 38 new victims. In determining the metric, Jonathan Reed's team relied on an article by Chinese authors dated January 21.

But the great weakness of the work consisted in the fact that in the early stages of the spread of any new disease with "usual" symptoms, the number of those who fell ill with it was underestimated. Fever, dry cough and rapid fatigue are typical symptoms of various diseases, and many will not go to any doctor with them. As often happens, some of us begin to want to go to the hospital only when they are already seriously taken.

But when the wave of information about the epidemic spread through TV and the Internet, when bulldozers began to bulldoze soil on the roads leading to Wuhan, then many people rushed to register their problems at the hospital, showing a sharp but short surge in the "infectivity index". Now suddenly there are few patients, then there are many at once.

However, the latest data on the "index of infectiousness" 2019-nCoV is completely different.As noted by the same Jonathan Reed, the "infectivity index" there is only 2, 5 (the middle of the range 2, 4-2, 6). It seems that 3, 8 and 2, 5 are slightly different numbers. In fact, with an index of 3, 8, one patient, having started only ten cycles of infection, is able to infect more than 627 thousand people. And with an index of 2, 5 - only 9, 5 thousand.

The difference, as we can see, is dozens of times - so great that now Reed's work is only of historical value. The author, however, plans to update it in order to take into account the real "infectivity index". But until then, we can confidently say: the forecast of his group is not particularly valuable - and that's to put it mildly.

Why did this virus appear in China and why is it so mildly contagious?

There are many amusing explanations circulating on the Web as to why all these SARS and the like so often occur in China and not elsewhere. Someone says that the Chinese simply do not follow hygiene enough, someone - that there is bad medicine, someone - that they eat too much raw meat and exotic animals. All this is not entirely true.

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Let's start with the basics. The Chinese have good hygiene: they invented toilet paper and established its widespread production in an era when the ancestors of everyone reading this text did not think about the problem further than burdock (not very common in winter). They also do well with medicine: life expectancy there is almost the same as in the United States and is much higher than in Russia, despite the lower GDP per capita.

Not very deep fried meat is eaten in many countries, including the States, but this does not make them a source of epidemics. To understand what exactly makes the PRC a source of a viral (and not only) deadly infection, you need to understand where on Earth viruses live well.

Viruses are organisms (however, some scientists do not consider them alive in the full sense of the word) that have an extremely high ability to change quickly. They have the highest mutation rate of any known organism, so they can constantly present slightly different versions of themselves. Such is, say, the flu: due to the ultra-high rate of mutations (more only in HIV), it bypasses vaccines created against strains of the same flu, but of past years.

To achieve this powerful variability, viruses use mechanisms that we humans lack. Our diversity of genes is supported by sexual selection: women are more attracted to men whose leukocyte antigens are least similar to the genes of this woman (ladies very accurately distinguish such men by their smell).

Viruses and bacteria do not formally reproduce sexually, but, in fact, a virus can often exchange genetic material with another virus. It is not always clear how exactly they do this, because it is difficult to observe such processes. In bacteria, this is done with the help of sex pili (they are called sex pili due to their distant similarity with means of sexual reproduction) pili, protein filaments on the surface of the bacteria. For viruses, the mechanisms should be much simpler.

But their essence is the same. In general, it is the same as that of us, organisms with sexual reproduction: the exchange of part of the genetic material. Just as small groups of people risk degeneration due to insufficient genetic diversity, so among infectious agents, the diversity is higher, the more around other organisms with which they can exchange genetic material.

For viruses and bacteria, the task is simplified by the fact that they can exchange it not only with representatives of the species, but also with anyone. By the way, in fact, such a horizontal transfer of genes from another species is possible in humans, only on a modest scale.

All this means that China is a promised land for infectious agents. More carriers - more opportunities to maintain the genetic diversity of the virus itself. And the point is not only in the high population density (in India it is not less), but also because it is warm and humid there.Because of this, many mammals and birds in China can live in a very small territorial area. This is important: the presence of many warm-blooded living species is a necessary condition for the ripening of really terrible epidemics.

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The fact is that the virus itself, which has been “cohabitating” with a person for a long time, cannot be too dangerous for him. The measles virus has been causing our illness for about a thousand years (before that, it parasitized on livestock). And already during this time, the probability of dying from it dropped to one person in a thousand without good treatment, and even lower - in the presence of the latter.

The HIV virus is much more terrible for us: without treatment, the majority die in ten years. But this is only because the transfer of the virus from the green monkey to humans happened a few decades ago (most likely, this trouble would not have happened if it were not for some frivolity of sexual behavior in Africa).

But if you ask a virologist to name a massive virus that would give a high probability of death, but at the same time would live with a person for at least thousands of years in a row, he will think. The reason is that the war with the host species is not profitable for the virus. It is much easier to quietly multiply inside it, without undermining the work of the host organism by excessive reproduction.

It's another matter if the virus has recently "spread" to our species from another species. It has not yet settled down in the body of the new host, so the host's immunity cannot suppress the virus really effectively, and the virus itself has not particularly adapted to the new "home", which causes great harm to it.

For example, this happened with the flu virus thousands of years ago or smallpox (we picked them up from livestock). Sometimes the virus does not cause a serious illness (more severe than the flu) in the local population, with whom it has been “cohabiting” for a long time, but it will be fatal for the newcomers.

This was the case with yellow fever, which "jumped" on people through mosquitoes from other primate species in Africa, deadly for Europeans, but relatively safe for Africans in areas where this disease is common.

China is a place where there are many species of mammals, in terms of temperature close to us humans. In the case of 2019-nCoV, bats were such a reservoir species, and they also served as the source of the closely related coronavirus that causes SARS.

Other places in the world are not so well suited. India has a smaller variety of mammalian species that can infect humans relatively easily. In Africa, the diversity is even greater, but the population density is lower than that of China and there is no means of quickly moving huge masses of people.

Recall that the outbreak of 2019-nCoV fell on the eve of the Chinese New Year, when hundreds of millions of Chinese are rapidly moving around the country in high-speed trains, which are more there than in any other part of the world.

As we can see, the PRC has created ideal conditions for the emergence of new viral infections. Of course, this is helped by the exotic tastes of local residents, who for some reason eat bats. But not much: the main factor here is precisely the wide variety of sources of new viruses and excellent long-distance mass transport, which simplifies the spread of infection.

How will the virus respond in life?

We have already noted above: epidemiologically, 2019-nCoV is moderately dangerous. A mortality rate of 2.35% with a base "index of infectiousness" of 2.5 is more likely SARS (fewer than a thousand victims) or Middle East respiratory syndrome 2012-2018 (two thousand victims) than influenza. Recall: in the world, tens of millions are infected with it a year, at least a quarter of a million die every year from its complications.

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But from an economic point of view, the coronavirus will definitely cause - and has already caused - big problems. The fact is that it is China that is the largest economy in the world, more than a quarter larger than the US economy. China accounts for 20 percent of world GDP in PPP terms, which means that even small, temporary, but rather sharp fluctuations there can noticeably affect the world as a whole.

This is especially important now, in the era of the influence of stock exchanges on the real economy.One significant blow to the nerves of brokers and stockholders - and they can arrange a stock market panic, which in itself can trigger a recession in the real sector of the economy.

Meanwhile, there are already grounds for such panic. During the Chinese New Year, the population spends much more than usual - more than we do during the New Year period (similar to China's situation in the United States at Christmas). This year's consumption surge was nowhere near as strong. Wuhan was closed, the subway was stopped there, the movement of people between cities (domestic tourism in China is the most popular) went down sharply.

Tourism yields to the Chinese economy strongly over a trillion dollars a year. The system of quarantines and recommendations to restrict movement can hold out until the end of the epidemic - and this, according to past experience with SARS, up to a couple of years. That is, we are talking about losses of hundreds of billions of dollars a year or even more.

The squeeze in consumer activity due to fewer visits to restaurants and public spaces can be just as dangerous. The PRC is a major importer of energy resources, foodstuffs and much more. A downturn in this economy could trigger a compression cascade around the world.

And the exchanges have already responded. Over the past day, Asian and European countries fell by 2%, in the US - by 1.5%. It is likely that Donald Trump, who has elections this year, will try to rectify the situation. The States are able to pump up the markets with money supply and prevent a crisis. However, the marked nervousness in the global economy is likely to persist for many months. And even those countries that are not directly affected by the epidemic will feel this.

UPD. The article is supplemented in connection with the new information that has appeared.

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