The researchers explain why the COVID-19 test is positive after recovery
The researchers explain why many people who had COVID-19 continued to have coronavirus RNA detected in the RT-PCR tests weeks or months after recovery. Scientists from the Whitehead Institute for Biomedical Research, the National Cancer Institute and the Massachusetts Institute of Technology offer their answer through the study now published in the Proceedings of the National Academy of Sciences.
The study shows that genetic sequences from RNA virus SARS-CoV-2 can be integrated into the genome of the host cell by reverse transcription. Then these parts of the genome are “read” in the RNA and as a result are detected by PCR test.
“The causative agent of COVID-19 is not the only virus that is integrated into the human genome. About eight percent of our deoxyribonucleic acid consists of remnants of the viruses. Some, called retroviruses, replicate through integration into DNA.
“SARS-CoV-2 is not a retrovirus, so it does not need reverse transcription for replication. However, non-retroviral RNA virus sequences have been found in the genomes of many vertebrate species, including humans, ” as per Naked Science which quotes the study’s first author, Ligua Zhang of the Whitehead Institute.
To test the hypothesis, the scientists conducted an experiment in the laboratory where they infected the human cells with coronavirus and two days later sequenced their DNA to see if it contains traces of genetic material of the pathogen.
For greater reliability, three different sequencing methods were used. As a result, the genetic material of the virus was detected in all samples, although none of the fragments would be sufficient to reproduce live SARS-CoV-2. The researchers then examined the DNA flanking the small viral sequences to understand the mechanism by which they got there.
Of course, to determine exactly how common this phenomenon is in real life, you will need more data. Probably only some human cells undergo any viral integration. If you take another RNA virus that is inserted into the genome of the host cell, then only 0.001-0.01 percent of infected cells would contain the embedded DNA of the pathogen. The frequency of SARS-CoV-2 integration in humans is currently unknown.
“The proportion of cells that integrate can be very small. But even if it rarely happens, millions of people are already infected, aren’t they? ”The scientists added.
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