It is a package of microscopic genetic material surrounded by a layer of protein and measures only one-thousandth of a human hair.
However, this lethal virus, called SARS-CoV-2, it has already spread to almost every country in the world and has infected more than half a million people since it was identified in China in December 2019.
Viruses such as this one, of the family of coronaviruses, which can cause illness in animals.
You know seven, including the SARS-CoV-2, that have jumped from animals to humans.
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And have been responsible for many of the outbreaks of diseases most destructive in the historyas the influenza pandemics of 1918, 1957 and 1968 and the outbreak of SARS, MERS and ebola.
But the experts agree that you may have never seen a pathogen so insidious as this new coronavirus.
What is it that makes the SARS-CoV-2 attack human cells and spread with such efficiency?
The entrance to the cell
Several studies are investigating which are the mechanisms at the biological level the virus uses to infect so easily to human cells.
Some scientists are focusing on the calls spikesproteins in the form of a tip protruding from its surface, forming a crown.
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Other studies are studying the “front door” that the virus uses to enter cells.
“Coronaviruses have that name for the spike proteins protruding from their surface, and these spikes are the ones that adhere to the cell to go to it,” she explains to BBC World Panagis Galiatsatos, professor of pulmonary medicine and intensive care, School of Medicine, the Johns Hopkins University.
The main mission of the virus once it enters the body is to create copies of itselfand to do that you need to find a way to enter the cells.
“The common cold virus, the 2003 SARS and the MERS, they all have those ears, and that determines how you will enter the cell is which receiver will be used for this purpose”, explains the expert.
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Some studies have shown that the SARS-CoV-2 “sneaks” by a receptor -or protein – called ACE2.
This protein is found in many parts of the human body: in the lungs, heart, kidneys, and intestine, and its main function is to reduce the blood pressure.
“The ACE2 is on the surface of the cell and when the virus recognizes it and adheres to it and thus enters the cell”, explains to the BBC’s Sarah Gilbert, professor of vacunología of the University of Oxford in the United Kingdom.
“Once you are inside, use the machinery of the cell as a factory to make copies of itself and of its genetic material. After escaping the cell, which is only a shell, and the virus, along with its thousands of copies, they are ready to begin to infect other cells.”
Respiratory viruses, such as the common cold, tend to breed in the nose and in the throat, where it can be spread easily by coughing or sneezing.
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But there are other viruses that breed only in the lower respiratory tract, in the lungs, where it is passed with less ease, but are much more dangerous.
The SARS-CoV-2, however, has a crucial feature: it is both in the upper respiratory tract, spreading with coughing, as in the lower, producing a condition in the lungs which can be fatal.
“The ACE2 receptor is very abundant in the body and is found in many of our bodies”, explains the professor Galiatsatos.
“Is in the cells of the mouth, the esophagus, the kidneys, the heart and in the gastrointestinal tract, that is why we have seen some patients with nausea and diarrhea.”
“But what worries us more is that these receptors are also in the cells of the alveoli, the delicate air sacs in the lungs where the gas transfer”.
When the virus damages these cells, explains the expert, are some of the most common symptoms that have been seen with covid-19: breathing problems, and coughingthat occurs when the lungs are trying to get rid of the infection.
Symptoms and infection
One of the main differences of the SARS-CoV-2 with other coronaviruses, such as the 2003 SARS or MERS, is that these recent viruses are adhered to more cellular receptors and are therefore reproduced more quickly.
This was causing the symptoms of the disease appear much faster, and the patients could be isolated without causing so many infections.
With the new coronavirus the symptoms do not appear immediately and people can have the virus and propagate it without signs of the disease.
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“SARS (2003) was a virus that was reproduced in the lungs and not transmitted as easily because the symptoms appeared quickly and the patient could isolate themselves”, she explains to the BBC, professor David Hymann, an expert in infectious diseases who led the response of the World Health Organization (WHO) during the epidemic.
“But all viruses are different, and this new virus seems to be very adapted to spread easily in humans“.
“We believe that a person can begin to infect others before symptoms appear, perhaps a day before, and then continues to propagate the virus for at least seven days,” he adds.
It is here where the true danger of the SARS-CoV-2, and it is for this reason that health authorities are placing so much emphasis on the social distancing.
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The virus can only survive if it finds a new host to infect. When a person stays in their house for 14 days eliminates the chances of passing the virus to someone else.
“For now this is the only thing that we can do. Is trying to find a vaccine or an effective drug, but the march of science is not as rapid as we would like and all of this takes time,” says Panagis Galiatsatos.
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“In the book “the art of war” Sun Tzu says that to win the battle you must know your enemy. But when you realize how incredibly clever he is your enemy, this gives you a lesson of humility“.
“And this is what I would say about this virus”.
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