AN INTERNATIONAL team of scientists has found evidence that the virus that causes COVID-19 infects cells in the mouth.
The team was led by researchers at the US National Institutes of Health (NIH) and the University of North Carolina at Chapel Hill.
It has been previously known that the upper airways and lungs are primary sites of infection from SARS-CoV-2, the virus that causes COVID-19.
There are indications as well that the virus can infect cells in other parts of the body such as the digestive system, blood vessels and the kidneys.
The new study shows that the virus infects cells in the mouth as well.
This may explain why oral symptoms such as taste loss, dry mouth and blistering have been observed in COVID patients.
It is possible that the mouth plays a role in transmitting the virus to the lungs or digestive system via the infected cells of saliva.
This new knowledge could assist health authorities develop strategies to lessen and control COVID transmission and help them better prepare for the next pandemic.
“Due to NIH’s all-hands-on-deck response to the pandemic, researchers at the National Institute of Dental and Craniofacial Research (NIDCR) were able to quickly pivot and apply their expertise in oral biology and medicine to answering key questions about COVID-19,” said Dr. Rena D’Souza, Director of the NIDCR, a branch of the NIH.
“The power of this approach is exemplified by the efforts of this scientific team, who identified a likely role for the mouth in SARS-CoV-2 infection and transmission, a finding that adds to knowledge critical for combatting this disease,” said Dr. D’Souza, a dentist.
It is common knowledge that the saliva of people with COVID-19 can contain high levels of the SARS-CoV-2 virus. This is why saliva testing is nearly as reliable as deep nasal swabbing for detecting COVID-19.
What was unclear is the origin of the SARS-CoV-2 virus in saliva.
Among COVID-19 patients who have respiratory symptoms, the virus in saliva was thought to be part of the nasal discharge or sputum coughed up from the lungs.
However, it does not explain how the virus gets into the saliva of people who lack the respiratory symptoms, said Dr. Blake M. Warner, a dentist and Assistant Clinical Investigator and Chief of NIDCR’s Salivary Disorders Unit.
“Based on data from our laboratories, we suspected at least some of the virus in saliva could be coming from infected tissues in the mouth itself,” said Dr. Warner who led the study published online in Nature Medicine.
Another member of the international team was Dr. Kevin M. Byrd, an Assistant Professor in the Adams School of Dentistry at the University of North Carolina at the time the study was conducted. Dr. Byrd, a dentist, is now an Anthony R. Volpe Research Scholar at the American Dental Association Science and Research Institute.
Dr. Ni Huang, PhD, of the Wellcome Sanger Institute in Cambridge, United Kingdom, and Dr. Paola Perez of NIDCR, were co-first authors of the study.
The researchers found evidence of oral tissue infection and started to look at whether the tissues could be a source of the virus in saliva.
They found that in people with mild or asymptomatic COVID-19, cells shed from the mouth into saliva contained the COVID virus.
Then they tried to determine if the virus in saliva is infectious. They concluded it was possible that even people without symptoms might transmit the virus to others through saliva.
What is greatly significant in the study is the new knowledge that the mouth has a bigger role in the transmission of COVID-19 than previously thought.
“When infected saliva is swallowed or tiny particles of it are inhaled, we think it can potentially transmit SARS-CoV-2 further into our throats, our lungs or even our guts,” said Dr. Byrd.
To know more about the exact nature of the mouth’s involvement in COVID transmission, more research in a larger group of people needs to be done.
What the study revealed, however, was a previously underappreciated role for the oral cavity in COVID infection.
***
Dr. Joseph D. Lim is the former Associate Dean of the UE College of Dentistry, former Dean of the College of Dentistry, National University, past president and honorary fellow of the Asian Oral Implant Academy, and honorary fellow of the Japan College of Oral Implantologists. Honorary Life Member of Thai Association of Dental Implantology. For questions on dental health, e-mail jdlim2008@gmail.com or text 0917-8591515./PN
