Last week the who announced that soon will travel to China, the group of experts, whose task is to help scientists of this country to establish a natural focus of the novel coronavirus that claimed more than 580 already thousands of lives around the world. About it writes BBC.
This is done not in order to find the culprits in the outbreak of the global epidemic. The objective of the scientific expedition much more pragmatic: who, the international community wants is possible to prevent the recurrence of similar emergencies in the future.
In 2004, scientists have managed to prevent the epidemic of “atypical pneumonia” SARS is due to the fact that after the first outbreak, experts have determined the origin of infection traced her path to the natural focus, and as soon as the virus started again to walk among the people, he was able to quickly defuse.
Now scientists have made every effort to repeat this success with a novel coronavirus — although this time seemingly identical task turned to the practice of this puzzle that has repeatedly ringleader investigators to a standstill.
Despite the considerable similarity of the two viruses, SARS-CoV-2 proved to be much tougher nut to crack than its predecessor, and to unravel the mystery of its origin will not be easy.
But the experience of past epidemics tells scientists which direction we should work. Yes, and the new coronavirus, which six months ago was not even the names, of time to learn — albeit weak, but still enough to hope for success.
“Go and do not know where”
To prevent a recurrence of the epidemic, scientists can more accurately answer two questions.
First, where exactly — from a “natural reservoir” — it’s a new infection. Simply put, what animals in the wild carry the virus, potentially threatening another global epidemic.
Secondly, as this virus more recently affecting animals exclusively, “has crossed the species barrier” — that is, to have the ability to move from person to person. You need to understand that a mutation has caused this change and how likely that it will happen again.
“It is one thing when a virus is transferred between people: we have the same immune system, same anatomy, very similar genes, explains Samar Mehta, one of the leading experts of the laboratory of computational biology Sabeti Lab at Harvard University. But in order to go to the human from the animal, the virus must overcome a much higher “evolutionary barrier” that is very much changed. So it happens so rarely.”
Sabeti Lab scientists call a world center for viral genetics. In recent decades experts from this laboratory have deciphered the genetic code and identified the origin of several dangerous pathogens, including viruses, zika and Ebola. The result is that both these infections, the scientists were able to actually rein: now, if where-that begins the outbreak of viral fever, it is usually possible to pay off relatively quickly, not allowing to escalate into a full-blown epidemic.
“Each virus is its genome — specific DNA sequences or RNA. It is completely unique — so much so that it can be compared with a fingerprint,” explains Dr Mehta principle of the “virus detectives”.
“With each new infection the genome of the virus changes a little. Just a little bit, just a fraction of a percent — but this allows you to set between two positive communications, — the expert continues. And if my fingerprints and fingerprints of my brother do not have anything in common, my viruses and my neighbor are almost identical.”
Genome SARC-CoV-2 is a long sequence of RNA, consisting of about 30 thousand letters (nucleotides), following each other in strict order. So, when building each new copy of the virus, there are 30 thousand opportunities to make mistakes, randomly replacing one letter with another.
If such an error occurred, but the virus had lost the ability to reproduce, a new sequence of RNA will be played again and again yet again can’t go wrong with the Assembly already in some other place.
Due to this, genetics can fairly accurately recover the chain on which transmitted the infection to determine which patients had infected whom, and in what order. And therefore understand who was the first sick — the so-called patient Zero, marked the beginning of the epidemic.
Finding it, you can find and animal, from whom he contracted.
On this way went Chinese scientists, when they realized that in Wuhan, an outbreak of a strange disease, caused by a new virus.
They gathered all available at that time, patients samples of genetic material transcribed them and began to compare with each other, the positioning in the order of divergence of the viral genome.
The result has lined up several long branched chains, showing the path of transmission.
“This so-called phylogenetic tree of the virus. It shows in what order to place the main mutations,” explains Alina Chan, Professor at the Institute of broad, collaborative center for genetic studies of Harvard and MIT.
“The scheme is seen as one variation of the genome is separated by another, then grows it out the next branch and so forth, she continues. — In fact, it is a visual representation of the evolution of the virus”.
Professor Chan is one of the authors of the sensational articles about the origin of SARS-CoV-2 where it was stated that genetically, the new coronavirus is perfectly adapted to the transmission from person to person. So, the current epidemic may not be the last — if the wild virus shows up while unknown close relatives.
In her opinion, it is not excluded. Where did the virus, we do not yet know. To reduce the chain of infection in Wuhan to the same point from where started the spread of infection, geneticists have failed.
Such “initial points” — unrelated to each other — turned out to be five.
Despite the fact that to detect patient Zero failed, scientists do not lose hope sooner or later to establish a natural focus of infection in another way.
In early January, as Chinese scientists have decoded the RNA of the pathogen of an unknown disease (at the time he didn’t even name) and compared the result with the database, it became clear that almost 80% identical with the genome of SARS — the virus that has twice caused the outbreak of “atypical pneumonia” 2002-2004
To find the source of the first SARS, the CDC took almost six months, says Alina Chan. Similarly, when the chain until the first infected, the scientists found that several of them visited the local market where they sell wild animals, and realized that the most likely source of infection is there.
Testing the market took more than one month. Geneticists had in a row to check all the animals that could potentially be intermediate carriers of infection. In may 2003, their efforts were crowned with success: the identical virus was found in the body Himalayan civet.
“When at the end of 2003 happened re the SARS outbreak, scientists have some idea where to look for the perpetrators — continues Professor Chan. On learning that one of the first patients she worked as a waitress, epidemiologists immediately went to the restaurant where she worked. There they found civet, checked for virus — and the analysis gave a positive result.”
As a result of all the investigation was over a few weeks and a large-scale epidemic was averted.
“A later genetic analysis confirmed that the second outbreak was not the first echo, said Alina Chan. For a year the virus was indeed crossed the species barrier at least twice.”
Knowing that the current Wuhan coronavirus, a close relative of SARS, scientists realized that the search for his ancestor most likely also need in the local markets of wild animals. But who to test this again — do again civet?
The closest genetic relative of SARS-CoV-2, all in the same database, was RATG13 virus, discovered in 2013 from bats in Yunnan province. The genomes of two viruses coincided on 96.2%.
It was not a surprise to scientists. In 2007 published a review of scientific papers, which stated that in nature there is a constant “reservoir” of the virus, related to SARS — and they often carry it bats.
The authors warned: the probability is high that the virus will become a danger for people, so you need to prepare for new epidemics.
This time, however, work in Wuhan market has stalled. To the surprise of geneticists, all they found at the market animal samples were more distant relatives of the novel coronavirus than the one that was discovered six years ago a thousand miles away.
Later it turned out one more unexpected detail: the first of five confirmed cases of infection (those “first patients”) to communicate with the Wuhan market managed only one. It turns out that the other four picked up the infection somewhere else — maybe even in different places.
Anyway the basic version of scientists about the origin of the virus was not confirmed. Leading the market was a wrong track.
“The problem with Covid-19 lies in the fact that we still have not found the body of an animal such version of SARS-CoV-2, which would allow us to assume that people acquired the virus from animals — makes a helpless gesture Professor Chan. Yet, on the contrary, all the animals, which were found in SARS-CoV-2, got it from the people.”
Apparently, in the Wuhan market has only occurred the first case of mass infection of new virus. How it got there, and where and how long hid before, remains a mystery.
Scientists at University College London have calculated that the genomes of SARS-CoV-2 and its closest relative RATG13 diverged from a common ancestor not coincident 4% by some mutations, it would take about 50 years of natural evolution.
According to scientists, it is very unlikely. Rather, the new coronavirus has got this part of his genome, giving fragments of RNA with different virus in the body of some intermediate host.
Recombination of two viruses within one organism — the phenomenon is relatively rare, but fairly well studied. Due to this phenomenon, apparently, has crossed the species barrier first SARS, borrowing part of its genome from a virus Himalayan civet.
Intermediate host SARS-CoV-2 was long considered the pangolin, these animals had previously been detected virus that partially similar to the “missing” slice. It was assumed that SARS-CoV-2 got his main weapon — thorn a protein that makes the virus is contagious, allowing it to penetrate our cells.
However, perhaps that is just the opposite — protein and thorn went to pangolins from an ancestor of the current coronavirus.
Neither one of these versions cannot be ruled out completely. Maybe in time scientists will be other theories. According to Alina Chan, with confidence about the new coronavirus can only say one thing: genetically it is perfectly adapted to easily be transmitted from person to person.
“But at the moment we have no sufficient evidence for any particular scenario the adaptation of SARS-CoV-2, — she said. And it is unclear when such evidence will be found.”
Samar Meta am convinced that sooner or later scientists will be able to find answers to questions. The main thing is not to drop it — or the recurrence of the epidemic is inevitable.
It also considers and Aline Chan. According to her, all conspiracy theories of the origin of the virus long been refuted by scientists, but many continue to use them to their advantage, earning political points.
“Scientists around the world working tirelessly, trying to understand the biology and epidemiology of the virus, developing treatment options, vaccines and in General do everything to predict the possible development of the pandemic and eventually to cope with it. Never before has the scientific community been so unified in the face of common problems. But the question of the origin of SARS-CoV-2 has become so politicized that people forget about the real purpose: the answer needed in the first place in order to prevent new outbreaks of coronavirus in the future,” concludes Professor Chan.