Why are some positives from the Kovid-19 test a few months after recovery? – Health

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The most sensitive way to know if a person is infected or not SARS-CoV-2 This involves collecting a sample of secretions present in the throat and nose. Then, PCR is used to detect the presence of virus RNA in the sample. If the result is positive, the person is infected: This is the well-known PCR test. The problem is that, even after the person is cured, this test continues to give positive results in many cases.

This is because the RNA fragments of the virus remain in the person’s throat for months. But where will these fragments come from if the virus is eradicated by the immune system and the person is cured? Until now, it was believed that even after treatment, the remains of the virus will remain in the throat. Now it turns out that the interpretation is different.

The Sars-CoV-2 genome consists of an RNA molecule that is covered by a capsule, showing the spine in photographs. After invading a human cell, the RNA present in the virus is released and multiplied, producing a large number of other RNA molecules, which are converted into new viral particles. This new generation of viruses is released and infects other cells. In this way the virus spreads in the body.

We have known for many years that RNA molecules inside a human cell can be converted into DNA molecules and these DNA molecules can sometimes be inserted into the DNA of the host cell.

Knowing this, the scientists decided to investigate whether it happened with Sars-CoV-2 RNA. For that, they used a number of methods that include isolating the DNA of infected cells, sequencing that DNA, and testing whether fragments of DNA containing the Sars-CoV-2 sequence exist. Scientists have not only found many pieces of the virus in different regions of the genome, but they have found that the regions that bind insertion sites are typical of a mechanism that exists in all of us and that can transform RNA molecules into DNA Are and can include. Them in the genome

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It was also possible to demonstrate that these inserted fragments are not capable of producing new viral particles (and that is why the individual remains fine), but do produce RNA fragments that can be detected in PCR tests.

These findings suggest that, in many people, the virus continues to invade cells and spread throughout the body until it fights the immune system, also entering the genome of fragments of infected cells of its genome. Can – After being cured, the body continues to produce these pieces of RNA and protein as long as the cells that have been infected and their descendants remain in our body. These fractions of RNA are detected by PCR testing in those who have already recovered.

It is not yet known whether this phenomenon has any consequences other than generating positive PCR tests, but scientists suggest that these fragments produced may serve as a constant stimulus to the immune system or in the presence of symptoms May include, in some people, persist for months after the infection ends (the so-called Long Kovid). This phenomenon is not unique to Sars-CoV-2, it has already been found in infection by other viruses.

The fact is that, after recovering from an infection, our body undergoes two changes: our immune system begins to produce antibodies and cells capable of fighting the virus and fragments of SARS in the genome of part of our cells Seems to be- COV-2. This finding may have important implications or may be just an explanation of why some people have positive CRP tests after recovering. It is too early to know.

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MAIS Information: Reverse-transcribed SARS-COV-2 RNA can integrate into the genome of cultured human cells and be expressed in patient-derived tissues. Prof. C. met. ACAD. Sci. USA https://doi.org/10.1073/pnas.2105968118

* He is a biologist, PhD in cell and molecular biology by Cornell University and author of the arrival of the new coronovirus in Brazil; Lotus leaf, mosquito slider; And the long march of cannibal cricket

About the author: Muhammad Wayne

Wayne is a reporter who covers everything from oil trading to China's biggest conglomerates and technology companies. Originally from Chicago, he is a graduate of New York University's business and economic reporting program.

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