A positive (L) and a negative antibody test for covid-19 are pictured at a pharmacy in Strasbourg, eastern France, on July 15, 2020. Photo: Frederick Florin/AFP (Getty Images)
New research this week seems to confirm the suspicion that the coronavirus can infect many parts of the human body, not just our respiratory tract. It also found that the virus can sometimes linger in the body even after a person’s initial symptoms have subsided. The preliminary findings may also shed light on the complex chronic condition known as long covid experienced by some survivors.
SARS-CoV-2 is primarily considered a respiratory virus, much like influenza or other human coronaviruses. In mild cases, the acute symptoms tend to involve the upper respiratory tract, while more severe cases are often associated with lung infection and pneumonia. But evidence from the lab and in patients has suggested that the virus can travel through the body and infect other tissues as well, thanks to the receptors it uses to hijack cells. Recently, for example, scientists found it evidence that the coronavirus can easily infect fat and immune cells.
The scientists behind this new study, mostly from the National Institutes of Health, say their research is the most comprehensive to date on how well the coronavirus can infect different parts of the human body and brain. For this, the researchers performed complete autopsies on 44 people infected with the corona virus. In all but five cases, the infection was directly involved in the person’s death.
Overall, the team found abundant signs of the coronavirus outside the respiratory tract, both early and late in the infection. The presence was definitely highest in the airways and lungs. But they also found viral RNA in the cardiovascular tissue of nearly 80% of the patients; in the gastrointestinal tissue of 72% of the patients and in the muscle, skin, adipose tissue (fat) and peripheral nervous tissue of 68% of the patients. In all 85 body parts and body fluids they studied, the virus could be found — at least some of the time — in 79 of them, including the brain. And they found traces of viral RNA throughout the body and brain months after symptoms started, up to 230 days in the case of one patient.
“Our data prove that SARS-CoV-2 causes systemic infection and can persist in the body for months,” the authors wrote in their paper, which was released as a pre-print Sunday, but is being reviewed for publication in the journal Nature, according to Bloomberg News.
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There are important limitations to this research. First, the cases clearly involved people who were seriously ill with Covid-19. But even in the few cases where someone had mild or no covid-related symptoms, the virus could still be found throughout the body, the authors noted. The study was also conducted between April 2020 and March 2021, a period when relatively few people were vaccinated. So it’s possible that people with some immunity could prevent the virus from infecting the body as thoroughly as these patients (the paper didn’t mention anyone being vaccinated). The emergence of some new variants of the virus, such as Delta and Omicron, since March may complicate the picture.
That said, the findings give us a clearer picture of how acute infection by SARS-CoV-2 works and how it can continue to cause problems after the initial illness seems to disappear. some experts to believe that at least some cases of long-term covid can be attributed to ongoing infection. But while these findings provide strong evidence that long-term infections do occur, they also raise new questions.
For example, the team found little evidence that the presence of the virus outside the lungs was associated with direct inflammation or other virus-related damage to cells, even with ongoing infections. That’s essential because inflammation is one of the most common ways the body can chronically damage itself, and many experts believe it plays an important role in long-term covid symptoms. In some cases of persistent infection, the authors noted, the virus may have been too defective to continue replicating, which may explain why the body didn’t respond to it like a typical infection. This finding doesn’t rule out the possibility that the virus is still doing damage when lingering in the body, but it adds another wrinkle to the long-term covid mystery that scientists will have to continue studying.
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