Covid: What happens to our bodies each day from coronavirus infection - BBC News BBC Homepage

Covid: What happens to our bodies each day from coronavirus infection – BBC News BBC Homepage

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André Biernath BBC News Brazil

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An individual blowing his nose, his face hidden

In recent weeks, cases of covid-19 have increased in several countries around the world, mainly due to the circulation of more infectious variants and the relaxation of protective measures.

How does Sars-Cov-2, the coronavirus responsible for the current pandemic, spread so easily?

In this report from BBC News Brazil, we explain the “path” that the virus takes in our body and what happens every day from the moment we come into contact with the pathogen.

Before going into details, an important caveat: the dates presented are only average estimates, based on information published in scientific studies and reviewed by national and international health agencies. These deadlines may vary, more or less, in specific cases.

Day 0: infection

It all starts when we are in close contact with someone who is already infected with the coronavirus.

When this person speaks, sings, coughs or sneezes, they release small droplets or aerosols of saliva carrying Sars-Cov-2 particles.

The amount of virus varies greatly from individual to individual. “Some have a low load, 10,000 viral copies per milliliter of saliva,” said virologist José Eduardo Levi, research and development coordinator at Dasa Laboratories.

“The average load varies between 10,000 and 1 million particles, but we see some that carry up to 1 billion viral copies per ml”, compares the specialist, who is also a researcher at the Institute of Tropical Medicine of the University of Sao Paulo.

These tiny infected droplets can be squirted directly onto our face, or remain airborne, “wandering” in the environment for minutes or even hours (in a dynamic very similar to that of cigarette smoke), depending on the circulation of the ambient air in each place.

In this second case, we ourselves inhale these aerosols during breathing.

And this is where the infection process really begins. Sars-CoV-2 uses spike (also called spike or protein S), which is on the surface of its structure, to connect to receptors on mucous cells in the nose, mouth, and even eyes.

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Artistic illustration of the Covid virus

From there, it will begin the routine common to all viruses: invade the cell and use all the biological machinery to constantly create new copies of itself.

“In this replication, it produces 100 to 1,000 new viruses in a single cell,” Levi estimates.

“It’s such a large number that the cell can’t handle it, it bursts and dies. These viruses are then released and will repeat this process in neighboring cells.”

This massive replication is also linked to the emergence of variants of the coronavirus. Not all specimens are identical and some have significant genetic mutations.

While this genome modification is of any benefit to the virus, it paves the way for the emergence and spread of new strains of concern, such as the well-known Alpha, Beta, Gamma, Delta and Omicron strains.

Days 1, 2 and 3: incubation

After Sars-CoV-2 has managed to invade the first cells of our body, the next step is to “gain ground” and broaden its spectrum of action.

The thousands of copies released by each invaded cell progress further and further through the body: they begin to work on the surface of the face, then enter the nose, down the throat and finally reach the lungs.

This period of silent evolution, during which the presence of the virus generates no signal, is known to experts as incubation.

“And we have noticed in recent months that the incubation time for new variants has decreased,” observes virologist Anderson F. Brito, a researcher at the Instituto Todos pela Saúde in Brazil.

According to a report by the UK Health Security Agency, incubation of the Alpha variant lasted an average of five to six days.

During the Delta lineage wave, this window was reduced to four days.

With Omicron, the period between viral invasion and onset of symptoms has been further reduced to just three days.

In other words, whereas it used to take almost a week for a person to come into contact with an infected person and show the typical symptoms of covid, this process is now much faster and can happen almost from day to day.

It should be mentioned that the incubation time can vary: in some cases, the symptoms appear up to 14 days after the first contact with the virus.

Days 4 to 14: onset and progression of symptoms

By progressing through the upper respiratory tract (nose, mouth and throat), the virus eventually attracts the attention of our immune system, which launches a counterattack.

The first line of defense involves cells such as neutrophils, monocytes and NK (natural killer) cells, as detailed in a paper published in 2021 by two researchers from Zhejiang University Hospital, China.

Eventually, other immune units come into play, such as T cells, which coordinate a more organized response to viral invasion, and B cells, which release antibodies.

But what is important here is that the symptoms appear in some people precisely because of this immune reaction: runny nose, cough, fever and sore throat are all attempts to eliminate the virus from the organism and an effect of the ceaseless work of so many cells.

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A person who coughs up droplets of saliva

But how long does the discomfort persist? This period can fluctuate considerably.

“It depends a lot on the individual. There are people with few symptoms who, after four or five days, are already recovered. In others, the same symptoms take longer to pass”, explains Nancy Bellei, infectiologist and virologist and professor at the Federal University of São Paulo.

“In general, the tendency is that the worst symptoms, such as sore throat and fever, last about three days,” says the specialist, who is also a member of the Brazilian Society of Infectious Diseases.

“After this period, it is normal for milder manifestations, such as runny nose and cough, to persist for seven to ten days,” she concludes.

At this stage, it is important to stay isolated and limit contact with others as much as possible.

From an individual point of view, resting and staying well hydrated is essential to ensure good recovery and give the body a “chance” to react well.

Taking some simple remedies for the discomforts of the infection, such as fever and pain, can also help.

“If, 72 hours after the onset of symptoms, you have difficulty breathing or if the fever persists, you should consult a doctor,” suggests Ms. Bellei.

This message is even more important for those who may suffer from more serious cases of covid, such as the elderly, the chronically ill and patients with compromised immune systems.

From a collective point of view, staying isolated is essential to cut the chains of transmission of the virus in the community and stop the increase in cases.

If you must go outside, wear a good quality face mask, as you are less likely to transmit the SARS-CoV-2 virus through the droplets and aerosols mentioned above.

From the 15th day: resolution of the infection (or appearance of lasting symptoms)

Up to two weeks after contact with the coronavirus, the immune system usually “wins the battle” and mostly stops its process of replicating and destroying cells.

This victory is of course facilitated by vaccination: the doses make it possible to safely “train” the defense units so that they know how to fight the pathogen before they even come into contact with it.

In some cases, unfortunately, the picture does not evolve as well: the virus manages to gain a lot of ground, reaches vital organs (such as the lungs) and generates a very serious inflammatory picture.

These situations usually require admission to the intensive care unit and intubation, as well as an increased risk of death.

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Some people with covid develop more severe forms of the disease

And even in patients who have recovered well, there is a non-negligible risk of long-term covid, marked by discomfort that lasts for months (or even years).

Although this area is still surrounded by many uncertainties, the US Centers for Disease Control and Prevention (CDC) estimates that up to 13.3% of people with covid experience symptoms lasting for a month or more.

About 2.5% report problems for at least three months.

Also according to the institution, more than 30% of covid patients who have been hospitalized, even after six months, still present with discomfort, ranging from fatigue and shortness of breath to anxiety and joint pain.

The CDC says it’s “working to better understand these post-COVID experiences and why they happen, including why certain groups are disproportionately affected.”

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