The profile of a murderer: this is the robot portrait of the coronavirus

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The researchers try to unravel the biology of the latest coronavirus, called SARS-CoV-2. The killer's profile is about to come to light. Scientists have learned that the virus has been able to evolve through multiple adaptations, making it far more lethal than the rest of the coronavirus humanity has encountered so far. Unlike its peers, SARS-CoV-2 can rapidly attack human cells at several points at once, with the lungs and throat being its primary targets. Genetic testing suggests that it has been hidden in nature for decades.

According to the journal Nature , of all the viruses that attack humans, coronaviruses are large. They measure 125 nanometers in diameter . With 30,000 base pairs, they also have the largest genome within RNA viruses, that is, those that use ribonucleic acid to multiply. Its genome is three times that of the AIDS or hepatitis C virus, and twice that of the influenza virus , influenza.

Coronaviruses are able to protect themselves from mutations that weaken them with a mechanism that corrects possible failures. That could be why antivirals like ribavirin, which have worked with viruses like hepatitis C, would have failed to cure SARS-CoV-2 infection. Medications weaken viruses by inducing them to mutate, but coronaviruses are able to prevent this.

Deadly ability

Coronaviruses have a special ability that makes them deadly: they are able to recombine RNA fragments with other similar coronaviruses. When two viruses of this type are able to end up in the same cell together, recombination "can create new versions capable of jumping into other species," says Andrew Rambaut, who is studying their evolution at the University of Edinburgh.

In bats this process often occurs. They harbor 61 viruses capable of making the leap to humans. Some species carry up to 121. Bats do not suffer the consequences. There are several theories that try to explain how bats' immune system defends itself. According to an article published in February, the bat cells infected by the virus are capable of harboring it without further ado .

The three coronaviruses that have caused the most problems for humans, SARS, Mers, and SARS-CoV-2, come from bats. But scientists think that the jump to humans always occurs through an intermediary. In the case of Sars, the intermediary is believed to be the civet, a mammal sold in China's animal markets. The origin of the disease that now paralyzes the world has yet to be defined. Although it shares 96% of its genetic material with a virus found in a bat in a Yunnan cave, they have important differences: that of Yunnan is not transmitted to people.

Nature explains that the studies that have come to light in recent months (some not yet reviewed), indicate that SARS-CoV-2 -or a very similar ancestor- has been hidden for several decades in some animal . The family line to the current coronavirus goes back more than 140 years. Then, sometime in the past, about 70 years ago, the ancestors of SARS-CoV-2 separated from the bat version. Rasmus Nielsen, an evolutionary biologist at the University of California, Berkeley believes this discovery is a warning. "We need to increase surveillance to anticipate the next emergency caused by a zoonotic transfer of a virus."

Efficient and lethal

The current coronavirus differs from Mers and Sars in that it is capable of affecting the upper respiratory tract and also infecting lung cells very efficiently. That gives you two ways to establish yourself. If someone close to you coughs and sends 10 viral particles, you could get a throat infection. If they are a hundred, they could reach your lungs, illustrates Shu-Yuan Xiao, a pathologist at the University of Chicago, Illinois.

Its attack capabilities would explain why people experience different symptoms. The virus can start in the throat or nose, cough, ruin taste and smell, and go no further. Or conversely it could go down the lungs and weaken them . "The process, how it progresses cell by cell to the lung, is not known," says Stanley Perlman, an immunologist at the University of Iowa.

People's response to the virus is also different. "The immune system of some is not able to prevent it from reaching the lungs. They cannot block it, " explains Clemens-Martin Wendtner, a German doctor who specializes in infectious diseases. The ability to reproduce and infect the upper respiratory tract has taken experts by surprise. A month ago, Wendtner published the results of several experiments in which his team was able to isolate the virus from the throats of nine infected people and demonstrated its high activity. That explains a crucial difference between their viral relatives. SARS-CoV-2 places particles from the throat into saliva , even before the first symptoms appear, making it easy to pass from person to person. The SARS coronavirus was much less effective: its infectivity increased when symptoms had been unleashed, making it much easier to contain.

Multi-organ damage

The damage from the new coronavirus doesn't just end in the lungs. Covid-19 infection accelerates an excessive immune response. The virus can also affect the intestines, blood, heart, sperm, eyes, and sometimes the brain. It also damages the kidneys, according to observations made on some patients, the virus could travel through the infected blood to various organs . But it is not yet clear what causes it: whether the virus or the immune storm unleashed on the body. "Autopsies will give the key. We will have more data soon."

Several researchers hope that the virus will weaken over time. It will mutate to coexist with the human being. Thus, it could be less lethal and have more opportunities to spread . But scientists have yet to find any signs of weakness, probably because of its effective genetic repair mechanism. "The Covid-19 genome is very stable, I don't see any changes caused by any mutations," explains Guo Deyin, who is researching coronaviruses at Guangzhou University.

Rumbaut doubts if the virus will become less harmful. "It doesn't work that way," he adds . "As long as you can successfully infect other cells, reproduce, and spread to other people, it doesn't matter if it causes host damage." There is a possibility of creating antibodies, "which will offer at least partial protection," according to Klaus Stöhr, head of Sars research at WHO. "Immunity will not be perfect: People who are reinfected will develop minor symptoms, such as a cold, and there will be rare examples of serious illness . People will have solid protection."

In one or two years the virus will continue to infect the population. "It is the most likely scenario. It will start to circulate steadily causing mild respiratory infections, " says Stöhr. That is the reason, he adds, "why vaccines will not be necessary."

According to the criteria of The Trust Project

• Coronavirus
• Diseases
• Respiratory diseases
• Infectious diseases

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