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BREAKING! COVID-19 News: Study Confirms That SARS-CoV-2 Infects And Replicates In The Salivary Glands And That The Mouth Is Also A Point Of Direct Entry For The Coronavirus

Publicado em 07 julho 2021

COVID-19 News: A new study by researchers from the University of São Paulo's Medical School-Brazil and the University of Michigan-USA have discovered that the SARS-CoV-2 coronavirus infects and replicates in the salivary glands of the human host. The study also shows that the mouth is also a point of direct entry for the novel coronavirus.

According to study abstract by the researchers, “The ability of the new coronavirus SARS-CoV-2 to spread and contaminate is one of the determinants of the COVID-19 pandemic status. SARS-CoV-2 has been detected in saliva consistently, with similar sensitivity to that observed in nasopharyngeal swabs.”

The study team conducted ultrasound-guided postmortem biopsies in COVID-19 fatal cases. Samples of salivary glands (SGs; parotid, submandibular, and minor) were obtained.

The team analyzed samples using RT-qPCR, immunohistochemistry, electron microscopy, and histopathological analysis to identify SARS-CoV-2 and elucidate qualitative and quantitative viral profiles in salivary glands. The study included 13 female and 11 male patients, with a mean age of 53.12 years (range 8–83 years). RT-qPCR for SARS-CoV-2 was positive in 30 SG samples from 18 patients (60% of total SG samples and 75% of all cases).

Ultrastructural analyses showed spherical 70–100 nm viral particles, consistent in size and shape with the Coronaviridae family, in the ductal lining cell cytoplasm, acinar cells, and ductal lumen of SGs. There was also degeneration of organelles in infected cells and the presence of a cluster of nucleocapsids, which suggests viral replication in SG cells.

Detailed qualitative histopathological analysis showed morphologic alterations in the duct lining epithelium characterized by cytoplasmic and nuclear vacuolization, as well as nuclear pleomorphism. Acinar cells showed degenerative changes of the zymogen granules and enlarged nuclei. Ductal epithelium and serous acinar cells showed intense expression of ACE2 and TMPRSS receptors. An anti-SARS-CoV-2 antibody was positive in 8 (53%) of the 15 tested cases in duct lining epithelial cells and acinar cells of major SGs. Only two minor salivary glands were positive for SARS-CoV-2 by immunohistochemistry.

According to the study team, “Salivary glands are a reservoir for SARS-CoV-2 and provide a pathophysiological background for studies that indicate the use of saliva as a diagnostic method for COVID-19 and highlight this biological fluid's role in spreading the disease.”

The study findings were published in the peer reviewed Journal of Pathology. https://onlinelibrary.wiley.com/doi/10.1002/path.5679

Detailed analysis of samples from three types of salivary gland obtained during a minimally invasive autopsy procedure performed on patients who died from complications of COVID-19 at Hospital das Clínicas, ie University of São Paulo's hospital complex, showed that tissues specializing in producing and secreting saliva serve as reservoirs for the novel coronavirus.

The study team said the discovery helps explain why the virus is so abundant in saliva and has enabled scientists to develop saliva-based diagnostic tests f or COVID-19.

First author Dr Bruno Fernandes Matuck, a PhD candidate at University of São Paulo's Dental School told Thailand Medical News, "This is the first report of a respiratory virus's capacity to infect and replicate in salivary glands. Until now it was thought that only viruses that cause highly prevalent diseases such as herpes used salivary glands as reservoirs. The discovery may help explain why SARS-CoV-2 is so infectious."

A past study by the same group had already demonstrated the presence of RNA from SARS-CoV-2 in the periodontal tissue of patients who died from COVID-19. https://pubmed.ncbi.nlm.nih.gov/33391625/

In March this year, Thailand Medical News also covered a study by American researchers from the U.S. NIH and also the University of North Carolina at Chapel Hill that also showed that the mouth and saliva were important components of SRS-CoV-2 infections of transmissions.

As a result of SARS-CoV-2 being more highly infectious compared with other respiratory viruses, the study team raised the hypothesis that it may replicate in cells of the salivary glands and hence be present in saliva without coming into contact with nasal and lung secretions.

Previous research had also detected ACE2 receptors in salivary gland ducts. The spike protein in SARS-CoV-2 binds to ACE2 in order to invade and infect cells. https://onlinelibrary.wiley.com/doi/full/10.1002/jmv.26045

Also most recently, other research groups have conducted studies in animals showing that other receptors besides ACE2, such as transmembrane serine protease 2 (TMPRSS2) and furin, both of which are present in salivary glands, are targets of SARS-CoV-2.

In order to test this hypothesis in humans, ultrasound-guided autopsies were performed on 24 patients who died from COVID-19, with a mean age of 53, to extract tissue samples from the parotid, submandibular and minor salivary glands.

The extracted tissue samples were submitted to molecular analysis (RT-PCR), which detected the presence of the virus in more than two-thirds. Immunohistochemistry ie a form of immunostaining in which antibodies bind to the antigen in the tissue sample, a dye is activated, and the antigen can then be seen under a microscope also demonstrated the presence of the SARS-CoV-2 virus in the tissue.

Lastly, examination under an electron microscope detected not just the presence of the virus but also its replication in cells and the type of organelle it uses to replicate.

Dr Matuck added, "We observed several viruses clustering in salivary gland cells, which showed that they were replicating there. They weren't in these cells passively.”

The study team now plans to see whether the mouth can be a direct point of entry for SARS-CoV-2, given that ACE2 and TMPRSS2 are found in various parts of the cavity, as well as in gum tissue and oral mucosa. In addition, the mouth has a larger contact area than the nasal cavity, which is widely considered the main way in for the virus.

Dr Luiz Fernando Ferraz da Silva, a professor at University of São Paulo and principal investigator for the project added, "We're going to partner with researchers at the University of North Carolina in the United States to map the distribution of these receptors in the mouth and quantify viral replication in oral tissues."

Dr Matuck further added, "The mouth could be a viable medium for the virus to enter the body directly.”

Also another investigative angle is to find out whether older people have more ACE2 receptors in their mouths than younger people, given the decrease in salivary secretion with age. Nevertheless, the study team found a high viral load even in older patients, who have less salivary tissue.

Dr Matuck said,"These patients had almost no salivary tissue, almost only fatty tissue. Even so, viral load was relatively high."

The study team concluded, “In conclusion, this study used the transcriptome data to analyze the expression levels for ACE2 and TMPRSS2 in salivary glands among a healthy population. Results from the scRNA-Seq analysis accurately located the expression and distribution of TMPRSS2 in salivary glands. TMPRSS2 is mainly expressed in salivary gland epithelial cells. These findings confirm that human salivary glands have a host cell receptor for SARS-CoV-2. This implies that the virus might gain entry into the salivary glands. However, the underlying mechanism remains unclear and should further be explored.”

Thailand Medical

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