One of the weirdest things about COVID-19 is the wide variety of symptoms people have. Some people go without symptoms, some end up with severe illness. Some get a cough or pneumonia, and others just a skin rash and fever. But one symptom stands out as the weird hallmark of this disease. Many patients lose their sense of taste and smell.
What gives?
COVID Affects Oral Health
We know SARS-CoV-2 can show up in saliva and oral mucosa. That’s why there is a cheek swab option for COVID tests, and why your clinicians here at Lake Baldwin Dental might have you rinse with mouthwash before we work on you. However, there is not as much definitive information as to how viral material ends up in the saliva. It was previously assumed that viral material could end up in the saliva by way of mucus from the lungs or nose. But that doesn’t account for the amount of detectable viral material in saliva from patients who had no symptoms like coughing or runny nose.
And then there’s the dry mouth and oral ulcers which also affect many patients who have lost their sense of taste or smell. Those symptoms can persist for months, long after other symptoms have gone away.
The COVID Virus Presents in Oral Tissues and Saliva
Research from the National Institutes of Health and University of North Carolina at Chapel Hill indicates that SARS-CoV-2 can infect the oral tissues directly. Researchers were able to isolate viral proteins in cells from salivary glands and gingival tissue.
To get a little more nerdy about it, there are two main factors which are needed to make a cell susceptible to infection by this virus: ACE2 receptors and TMPRSS2 enzyme. These two factors combine to make the cell permeable to viral RNA. Then, if a cell becomes activated, it will start making copies of the virus. Most viruses target only one or a few specific tissue types in the body. The lungs or the GI tract, for example.
It was therefore something of a surprise when researchers realized that gingival and salivary gland cells could be made to actively produce viral material. This likely accounts for many of the oral symptoms associated with COVID, as well as the loss of taste and smell, as both of these senses depend on flavor receptors in the mouth and oropharynx.
Viral Material in Saliva and Oral Tissue May Be Important in Spreading COVID
This also strongly suggests that SARS-CoV-2 can be spread through the saliva. In fact, the research team was able to isolate cells from the oral environments of infected patients and infect healthy cells harvested from uninfected patients.
Because active viral material can be found in the saliva of patients with even mild or completely asymptomatic COVID cases, we may now better understand why asymptomatic spread has been so much more of a problem with SARS-CoV-2 than with most other viruses. It is likely that the oral environment may serve as a sort of first portal into the body.
It may happen something like this: the virus takes up residence in the gum tissue and salivary glands; infected tissue sends viral material into the saliva, which is then swallowed or inhaled deeper into the body; then, viral RNA can find new portals for entry through the lungs and gut.
This pathway may also account for some of the myriad manifestations of the virus, from lung infections to diarrhea. And why so many people lose their sense of taste!
Good News for a COVID-Free Future?
The bad news is that this research is still fairly early in its process and much more work needs to be done. The good news is that these results may offer some potential therapies to combat oral COVID symptoms, and could help us find even more ways to limit the spread of this global pandemic.
In the meantime, keep your spit to yourself, Orlando!
