A possible explanation for repeated positive PCR tests even after surviving corona infection is provided by a study by US researchers: According to the study, in very rare cases small snippets of the coronavirus genome could be incorporated into the human genome. In the PCR test, this could simulate an infection – although the viruses have long since disappeared from the body, the scientists report in their preliminary publication, which has not yet been checked by independent researchers. Whole viruses that trigger a new disease or infect other people could not be formed as a result of the genetic takeover, the scientists write.

The number of people infected with the coronavirus is constantly increasing. This selection of articles gives an insight into the effects of the infection:

integration from RNA to DNA Colleagues rate the work as scientifically exciting and the processes presented as principally credible, but mostly see no biological significance of the processes shown. “However, it will be completely ruled out that the RNA vaccine will be rewritten and integrated into DNA,” emphasizes Joachim Denner from the Robert Koch Institute (RKI) in Berlin. With a view to the imminent start of vaccinations, this fear is occasionally expressed.

It is commonly said that an integration of the coronavirus genome into the human genome is not possible for biological reasons, because the genetic information is different Form: in the virus in the form of RNA, in humans in the form of DNA. Since the two molecules are chemically different, they cannot easily fuse with each other, so the coronavirus cannot “build” its genetic makeup into that of an infected person. “Integration of RNA in DNA is not possible due to the different chemical structure,” writes the Paul Ehrlich Institute.

Extreme circumstances – RNA of the virus rewritten into DNA The work of Researchers led by Rudolf Jaenisch from the Massachusetts Institute of Technology in Cambridge have now possibly shown that this is possible under extreme circumstances and, in very rare cases, may also happen after a natural infection. On the one hand, the scientists found fragments of virus genome in human DNA in genetic data from cells of infected people. On the other hand, they demonstrated in cell culture experiments that the cells can in rare cases take up virus genome if certain human genome segments are over-activated. This can happen through an infection. Through this activation, the RNA of the virus is transcribed into DNA and can then be incorporated into the human genome.

“Should it be claimed in the current public discussion that viral RNA as from the Sars-CoV-2 -Virus cannot be overwritten into human genomic DNA in principle, this is actually wrong. This is shown by the present study, “says Oliver Weichenrieder from the Max Planck Institute for Developmental Biology in Tübingen. The RNA converted and incorporated into DNA can later be converted back into RNA. But: “Such RNA is not infectious and can no longer produce a virus.” The results are by no means surprising. It has long been known that the overactivated genome segments in question can rewrite RNA and integrate it into the genome.

Possible protective mechanism – a number of interesting questions Because no new viruses are formed, the incorporation of the virus genome is biologically probably a one-way street, said virologist David Baltimore from the California Institute of Technology towards the magazine Science . It is also not clear whether the cells in humans that have absorbed the virus genome are retained for a long time or die. “The work raises a number of interesting questions.”

From an evolutionary point of view, it is conceivable that the incorporation of virus RNA is a protective mechanism of the body, write the US researchers themselves. The immune system could react to the built-in foreign genetic material and provide defensive weapons that are ready for use in the event of a real virus infection.

(bme)