NIH study finds coronavirus infects mouth cells, saliva

Medical studies finding possible long-term effects of COVID-19

This study followed patients who had a mild case of COVID-19 for up to nine months after recovery - and found about a third of them had persisting symptoms.

BETHESDA, Md. - A recent study by the National Institutes of Health found that SARS-CoV-2, the virus that causes COVID-19, may infect oral cells, which explains a variety of symptoms that occur in the mouths of coronavirus patients.

Researchers say half of all COVID-19 patients have experienced some oral symptoms, including the loss of taste, dry mouth and lesions.

Much of the way the disease spreads is through the mouth, including by coughing, breathing and talking.

NIH scientists said that before the recent study, they weren’t clear on whether the novel coronavirus could directly infect and replicate in the tissues of an individual’s mouth.

According to the study, which was published on March 25 in the medical journal Nature Medicine, researchers analyzed oral tissue samples from COVID-19 patients to determine if those specific samples were infected with the virus.

"In people with mild or asymptomatic COVID-19, cells shed from the mouth into saliva were found to contain SARS-CoV-2, as well as RNA for the entry proteins," according to an NIH news release.

Researchers exposed saliva from eight people with asymptomatic COVID-19 to healthy cells grown in a dish. They found that saliva from two of the volunteers infected healthy cells, suggesting that people who do not exhibit coronavirus symptoms could still transmit the disease through saliva.

Scientists then analyzed the relationship between various oral symptoms from COVID-19 and how the virus replicates and exists in saliva samples. They found that among 27 people with mild COVID-19 symptoms, people whose saliva was infected with the virus were more likely to report loss of taste and smell.

"Together, these findings suggest that the mouth, via infected oral cells, may play a bigger role in SARS-CoV-2 infection than previously thought," NIH researchers wrote.

NIH researchers said the two findings suggest that when the coronavirus infects the mouth it can transfer to the saliva and eventually infect the lungs when breathed in or swallowed.

"By revealing a potentially underappreciated role for the oral cavity in SARS-CoV-2 infection, our study could open up new investigative avenues leading to a better understanding of the course of infection and disease," said Dr. Blake Warner of the NIH’s National Institute of Dental and Craniofacial Research (NIDCR). "Such information could also inform interventions to combat the virus and alleviate oral symptoms of COVID-19."

This story was reported from Los Angeles.