2023-12-28 05:15:00
The SARS-CoV-2 virus, after causing the Covid-19 infection, quickly becomes undetectable, at most one to two weeks, in the upper respiratory tract and in the blood. Has the virus been completely eliminated from the body? The answer is negative.
A team from the Pasteur Institute has just confirmed, in primates, the persistence of the virus, via the analysis of biological samples from previously infected animals. This work was published on November 2, 2023 in the journal Nature Immunology.
Why did you research the persistence of the virus?
“We noticed that inflammation persisted for long periods in primates that had been infected with SARS-CoV-2. We then suspected that this inflammation could be due to the presence of the virus in the body,” summarizes Michaela Müller-Trutwin, head of the “HIV, inflammation and persistence” unit at the Pasteur Institute.
Indeed, the team was able to find the virus 6 to 18 months after infection, even though SARS-CoV-2 was undetectable in the blood and in the upper respiratory tract. Taken and placed in culture, these viral cells showed that they were still capable of replicating.
The trail of natural killer cells
We already know the ability of certain viruses to remain undetectable in the body. This is the case of HIV, responsible for AIDS. The virus remains hidden in viral reservoirs, capable of reactivating.
To understand the role of immunity to SARS-CoV-2, researchers focused on natural killer cells, also called NK. As a reminder, NK cells are lymphocytes of the innate immune system, capable of killing tumor cells but also cells infected by a virus.
According to the results of the study, in certain individuals, macrophages – these immune cells capable of ingesting foreign bodies – infected by the virus, became resistant to NK cells. In others, NK cells managed to adapt and destroy the virus. The Pasteur Institute then speaks of adaptive NK cells.
The viral reservoirs behind long Covid?
The researchers were able to observe that individuals who had a greater quantity of virus showed a decrease in NK cell activity and an absence of adaptive NK cells. Conversely, those in whom the virus was undetectable or barely detectable produced adaptive cells.
Is this mechanism at the origin of the formation of viral reservoirs and, consequently, long Covid? “We will begin a study on a cohort of people who were infected with SARS-CoV-2 at the start of the epidemic in order to find out if the viral reservoirs and the mechanisms identified are linked to cases of long Covid. But these results are already an important step in understanding the nature of viral reservoirs and the mechanisms that regulate viral persistence,” concludes Michaela Müller-Trutwin.
If long Covid is difficult to quantify, Public Health France estimated, according to the first results of a study published in June 2023, that 4% of the general population would suffer from a “post-Covid-19 condition”, or 30%. people infected with the virus (2.06 million people in total).
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