The new coronavirus lives in the mouth

SARS-CoV-2 enters the cells of the salivary glands and gums and multiplies successfully in them.

The SARS-CoV-2 coronavirus affects not only lung and bronchial cells. It is known that it can penetrate into intestinal cells, into the brain, into the kidneys, possibly into the testes, and into some other organs. Researchers from the US National Institutes of Health, along with colleagues from other scientific centers, have discovered another place where the new coronavirus can settle in us – this is the mouth.

The coronavirus is known to be found in saliva, and saliva analysis can be as reliable a way to detect SARS-CoV-2 infection as a nasopharyngeal swab. However, until now it was not very clear where the virus comes from in saliva. After all, he could well appear in the mouth from the same nasopharynx or together with mucus coughing up from the bronchi. On the other hand, SARS-CoV-2 was found in saliva even in those who had the infection without respiratory symptoms, who did not cough up anything.

To enter a cell, the virus needs two cellular proteins, ACE2 and TMPRSS2. By interacting with ACE2 and TMPRSS2, which sit on the outer cell membrane, the virus opens doors for itself inside the cell. If both genes are active in a cell, then with a high probability SARS-CoV-2 can penetrate into it. In an article in Nature Medicine both the ACE2 protein gene and the TMPRSS2 protein gene are said to be active in some cells of the salivary glands and gingival mucosa. Moreover, both genes were active here to the same extent as they are active in the cells of the nasopharynx, into which the virus obviously easily penetrates.

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The fact that the virus is able to live in the salivary glands was confirmed by the analysis of salivary gland samples taken from those who died from coronavirus infection and from seriously ill patients. There was so much viral RNA in these samples that it became clear that SARS-CoV-2 not only penetrates into glandular cells, but also multiplies successfully in them. The virus from the saliva of asymptomatic patients was tested for viability – and it turned out that it is quite capable of infecting healthy cells if they are treated with this saliva.

Finally, when the medical histories of several dozen almost asymptomatic patients with the virus in their saliva were analyzed, it turned out that they were losing taste and smell – although they had no other symptoms. In other words, SARS-CoV-2 not only enters the cells of the oral cavity (and the salivary glands belong to the oral cavity), not only multiplies in them, but also causes some of the clinical symptoms of COVID-19 coronavirus infection. The virus can use the mouth as an additional reservoir, not to mention the fact that living here, it is easier for it to move from person to person. However, in the oral cavity, it is not found in all patients, which means that you need to understand what factors help or push SARS-CoV-2 to settle in the mouth.

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