In some people, the coronavirus PCR test shows a positive result even though the infection occurred a long time ago. Researchers may have found an explanation for this.
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 coronavirus genetic material could be incorporated into the human genome.
This could simulate an infection in the PCR test – even though the viruses have long since disappeared from the body, the scientists report in their preliminary publication, which has not yet been reviewed by independent researchers. However, whole viruses that trigger a new disease or infect other people could not be formed as a result of the genome takeover, the scientists write.
Processes described as credible in principle
Expert colleagues judge the work to be scientifically exciting and the processes outlined to be credible in principle, but predominantly do not see any biological significance of the processes shown. “However, it will be completely ruled out that the RNA vaccine is transcribed and integrated into DNA,” emphasizes Joachim Denner of the Robert Koch Institute (RKI) in Berlin, for example. In view of the imminent start of vaccinations, this fear is occasionally expressed.
It is commonly said that integration of coronavirus genetic material into the human genome is not possible for biological reasons, because the genetic information is present in different forms: 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, so the coronavirus cannot “integrate” its genetic material into that of an infected human. “An integration of RNA into DNA is not possible, among other things, due to the different chemical structure,” writes the Paul Ehrlich Institute, for example.
Fragments of viral genome in human DNA
The work of researchers led by Rudolf Jaenisch of the Massachusetts Institute of Technology in Cambridge has now possibly shown that this is possible under extreme circumstances and in very rare cases may even happen after a natural infection. On the one hand, the scientists found fragments of viral genetic material in human DNA in genetic data from cells of infected people.
On the other hand, they proved in cell culture experiments that in rare cases the cells can take up viral genetic material if certain sections of the human genetic material are overactivated. This can happen, for example, as a result of an infection. This activation causes the RNA of the virus to be transcribed into DNA and can then be incorporated into the human genome.
Results not at all surprising
“Should it be claimed in the current public discussion that viral RNA such as from the Sars-CoV-2 virus cannot in principle be overwritten into human genomic DNA, this is in fact incorrect. This study shows this,” says Oliver Weichenrieder of the Max Planck Institute for Developmental Biology in Tübingen.
RNA that has been converted into DNA and incorporated can later be converted back into RNA, he said. But, “Such RNA is not infectious and can no longer produce a virus.” The results are by no means surprising, he said. That the overactivated genomic segments in question can rewrite RNA and integrate it into the genome has long been known, he said.
“The work raises a number of interesting questions”
Because no new viruses are formed, the incorporation of the viral genome is probably a one-way street biologically, virologist David Baltimore of the California Institute of Technology also told Science magazine. It’s also not clear, he said, whether in humans those cells that have incorporated viral genetic material are long-lived or die. “The work raises a number of interesting questions.”