Scientists find evidence that novel coronavirus infects the mouth’s cells

NIDCR Director Rena D’Souza, D.D.S., M.S., Ph.D. stated that the institute’s rapid pivot and application of oral biology and medicine knowledge to addressing critical concerns regarding COVID-19 was possible because of NIH’s all-hands-on-deck reaction to the epidemic. SARS-CoV-2 infection and transmission may occur via the mouth, as shown by the work of the research team who discovered this. This discovery provides important information for the fight against the illness. NIDCR’s Salivary Disorders Unit chief Blake M. Warner and Adams School of Dentistry assistant professor Kevin M. Byrd, D.D., Ph.D., led the study, which was published online on March 25, 2021 in Nature Medicine. Warner is a dentist, physician, and clinical investigator at NIDCR. Byrd is also a dentist and physician at UNC-Chapel Hill. The American Dental Association Science and Research Institute has named Byrd an Anthony R. Volpe Research Scholar. The study’s co-first authors were Ni Huang, Ph.D., of Cambridge, U.K.’s Wellcome Sanger Institute, and Paola Perez, Ph.D., of NIDCR.

Some researchers believe saliva testing may be almost as accurate for identifying COVID-19 as nasal swabbing for individuals with high amounts of SARS-CoV-2 in their saliva. Where the SARS-CoV-2 virus originates from remains a mystery to experts. COVID-19 patients with respiratory symptoms may have virus in their saliva that originates from nasal discharge or lung sputum. The virus may still enter the saliva of healthy individuals even if they don’t have respiratory symptoms, according to Warner. Based on our research, we believed that part of the virus in saliva came from infected oral tissues, according to Warner.

To test this hypothesis, scientists examined oral tissues from healthy volunteers in order to find mouth areas that might be infected with SARS-CoV-2. These cells have RNA instructions for producing “entry proteins,” which the virus needs to enter the cells. Vulnerable cells do not. Certain salivary gland cells and oral cavity-lining tissues had RNA for two critical entry proteins, including the ACE2 receptor and the TMPRSS2 enzyme. RNA for both ACE2 and TMPRSS2 was expressed in the same cells in salivary glands and gingival (gum) tissues. Because the virus is believed to need both entrance proteins to enter cells, this resulted in increased susceptibility. In areas known to be vulnerable to SARS-CoV-2 infection, such as the tissue lining the nasal passages of the upper airway, entrance factor expression levels are comparable, according to Warner.

Once the researchers had established that oral tissue samples from individuals with COVID-19 were infected with SARS-CoV-2, they searched for signs of infection in those samples. SARS-CoV-2 RNA was found in the salivary glands of slightly over half of the COVID-19 patients whose samples were obtained at NIH. Scientists found unique viral RNA sequences in the saliva of a deceased person and in the saliva of a person with acute COVID-19 who was still alive, indicating that cells were actively producing new copies of the virus. This strengthened the case for infection. To find out whether the virus in saliva came from oral tissue infection, the researchers looked for a source in the patient’s mouth. As it turned out, this was the case. SARS-CoV-2 RNA and RNA for the entry proteins were identified in cells shed from the mouth into saliva by individuals with moderate or asymptomatic COVID-19. Researchers exposed healthy cells produced in a laboratory to the saliva of eight individuals with asymptomatic COVID-19 to test whether the virus was contagious. Two participants’ saliva infected healthy cells, increasing the potential that even individuals with no symptoms may spread infectious SARS-CoV-2 via saliva.

Finally, the researchers collected saliva from 35 NIH volunteers with moderate or asymptomatic COVID-19 to examine the connection between oral symptoms and virus in saliva. People who had the virus in their saliva were more likely to suffer loss of taste and smell, indicating that oral infection may be the cause of COVID-19’s oral symptoms. SARS-CoV-2 infection seems to be more closely linked to infected oral cells than previously believed, according to the study’s authors. “We believe that swallowing or inhaling small particles of contaminated saliva may spread SARS-CoV-2 to other parts of the body, including the throat, the lungs, or the gut,” added Byrd. In order to validate the results in a broader population and to establish the precise nature of the oral cavity’s role in SARS-CoV-2 infection and transmission inside and beyond the body, further study will be required. “Our work may have opened up new research paths by showing an unappreciated function for the oral cavity in SARS-CoV-2 infection. This may lead to a better understanding of infection and disease progression. As a result of these findings, treatments to fight the virus and relieve COVID-19 oral symptoms may be improved “Warner made the statement.

Reference : NIH/National Institute of Dental and Craniofacial Research. (2021, March 25). Scientists find evidence that novel coronavirus infects the mouth’s cells: Findings point to a role for saliva in SARS-CoV-2 transmission. ScienceDaily. Retrieved October 4, 2021 from

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