Does the coronavirus infect the mouth?
12:45
(CNN) -
Researchers say they found evidence that the coronavirus infects the mouth, including inside the cheeks, in the gums and in the salivary glands.
When people swallow infected saliva, they could be spreading the virus to other parts of their body.
Their findings, detailed in the journal
Nature Medicine
on Thursday, could explain why so many infected people lose their sense of taste.
They also suggest that the mouth is an important source of the spread of COVID-19.
"When infected saliva is swallowed or small particles are inhaled, we believe that it can potentially transmit SARS-CoV-2 to our throats, our lungs or even our guts," said Dr. Kevin Byrd of the Institute of Science and Research at the American Dental Association, who worked on the study.
Saliva tests were already known to be a good way to detect infection.
However, the researchers had not studied 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.
What could be the link with the loss of taste?
The researchers analyzed oral tissue and discovered that cells inside the mouth carried the receptors that the coronavirus uses to infect them, including the ACE2 receptor.
They reviewed oral tissue samples from people who died from coronavirus and found the virus in about half of the salivary glands they tested.
The experts also tested people with mild or asymptomatic COVID-19.
In these tests they discovered that cells shed from the mouth into saliva carried active RNA.
This indicates that the virus was replicating in the cells.
They also exposed cells in a lab dish to the saliva of eight people with asymptomatic COVID-19 and managed to infect the cells.
This finding suggests that saliva may in fact be infectious.
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For the study, they collected saliva from 35 volunteers from the National Institutes of Health who had mild or asymptomatic COVID-19.
"In individuals with symptoms, the presence of SARS-CoV-2 RNA in saliva was positively associated with patient-reported 'loss of taste and smell," the researchers wrote.
This is how covid-19 alters the sense of smell 2:20
The study also found evidence that people who tested negative after a nasal swab sometimes continued to test positive on a saliva test.
This underscores that even if the virus is no longer in the nasopharynx - the upper part of the throat behind the nose - it could persist in saliva.
