Researchers said Thursday they found evidence that the coronavirus infects the mouth, including inside the cheeks, in the gums and in the salivary glands.
Their findings, detailed in the journal Nature Medicine, may explain why so many people infected with coronavirus lose their sense of taste. They also suggest that the mouth is a major source of the virus spreading.
“When infected saliva is ingested or tiny particles of it are inhaled, we believe that it can potentially transmit SARS-CoV-2 to our throat, lungs or even our guts,” said Dr. Kevin Byrd of the American Dental Association Science. and Research Institute, who worked on the study.
Saliva tests are known to be a good way to detect coronavirus infection, but researchers hadn’t looked to see why. The mouth, nose, sinuses, throat, and lungs are all connected, and the virus can spread to all of these regions in mucus that is drained or coughed up.
“We suspect that at least some of the virus in saliva could come from infected tissues in the mouth,” said Dr. Blake Warner of the National Institute for Dental and Craniofacial Research, one of the National Institutes of Health, who helped lead the study. study.
The researchers tested oral tissue and found that cells within the mouth carry the receptors, or cell gates, that the coronavirus uses to infect them, including the ACE2 receptor. They reviewed oral tissue samples from people who died of Covid-19 and found the virus in about half of the salivary glands they tested.
They tested people with mild or asymptomatic Covid-19 and found that cells shedding from the mouth into saliva carried active RNA, an indication that the virus was replicating in the cells. And they exposed cells in a lab dish to the saliva of eight people with asymptomatic Covid-19 and managed to infect the cells, a finding that suggests that saliva may be infectious.
They collected saliva from 35 volunteers working at NIH who had mild or asymptomatic Covid-19. “In symptomatic individuals, the presence of SARS-CoV-2 RNA in saliva was positively associated with self-reported ‘loss of taste and smell’ by the patient,” the researchers wrote.
The researchers also found evidence that people who test negative after a nasal swab sometimes continue to test positive on a saliva test. “These data highlight the possibility that the virus is shed from the nasopharynx but may persist in saliva, suggesting a sustained shedding of the virus from oral sites infected with SARS-CoV-2,” they wrote.