COVID-19 Causes Loss Of Taste, As Infection Targets Mouth Cells: Study

A team of researchers has discovered that COVID-19 causing coronavirus infects cells in our mouth, which results in the feeling of tastelessness, dryness and even blisters in some cases.

iStock

It is already established that lungs and upper airways are the hotspots for COVID-19 infection, however, this study offers clues that the virus can also infect cells in other parts of our body and affect areas like the digestive system, blood vessels etc.

Researchers were trying to find where the novel coronavirus comes from in the saliva. Sure, for people with respiratory symptoms, the sputum and nasal drainage could show a link, but this couldn¡¯t explain the presence in those individuals who lacked respiratory symptoms.

A deep-dive into oral tissues

To dig deeper, (study published in Nature Medicine) the researchers surveyed oral tissues from healthy individuals to identify mouth regions susceptible to SARS-CoV-2 infection. Vulnerable cells contain RNA instructions for making ¡®entry points¡¯ that the virus requires to enter the cells. RNA for two key entry proteins dubbed ACE2 receptor and TMPRSS2 enzyme was present in a small portion of salivary gland and gingival or gum cells.

RNA for the aforementioned enzymes was also seen in the same cells, indicating increased vulnerability as the virus is believed to need both entry points to gain access to cells. Moreover, researchers also found that the expression levels of the entry factors were similar to tissue lining in the nasal passages of the upper airway -- the common entry point for the novel coronavirus.

After confirming the parts of the mouth susceptible to SARS CoV-2, they looked for evidence of infection in oral tissue samples of people who had COVID-19. From the samples collected by NIH of dead COVID-19 patients, SARS CoV-2 RNA was present in over 50 percent of salivary glands they looked at.

Scientists also discovered specific sequences of viral RNA that showed cells were actively making new copies of the virus. After finding evidence of oral tissue infection, they looked to understand if those tissues could be a source of the virus in the saliva, which they found to be true -- people with mild or asymptomatic COVID-19 cells shed from the mouth into the saliva contained SARS CoV-2 RNA as well as RNA for the entry of proteins.

Paola Perez, PhD, Warner Lab, NIDCR

Is saliva infectious?

To test if this saliva is infectious, they exposed saliva from asymptomatic COVID-19 infected individuals against healthy cells from non-infected individuals in a dish and saw saliva from two of the volunteers to cause infection of healthy cells, raising the possibility that people without symptoms can also transmit infection with their saliva alone.

Next, to understand the relationship between oral symptoms and virus in saliva, the team collected saliva from a separate group of 35 NIH volunteers with mild or asymptomatic COVID-19. Of the 27 individuals who experienced symptoms, those who had the virus in their saliva were more likely to report loss of taste, smell.

Kevin M. Byrd, Anthony R. Volpe Research Scholar at the American Dental Association Science and Research Institute and one of the authors of the study, explains, ¡°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.¡±

Blame Warner, assistant clinical investigator and chief of NIDCR¡¯s Salivary Disorders Unit added, ¡°By revealing a potentially under-appreciated 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. Such information could also inform interventions to combat the virus and alleviate oral symptoms of COVID-19.¡±