Coronavirus progression is being studied and according to an international team of scientists COVID-19 or SARS-CoV-2 is found to infect the cells of the mouth. It is known that Lungs and Upper Respiratory tract is the common site or Primary site of infection of the virus along with other less commonly affected parts like the Kidneys, digestive tracts, blood vessels, etc. Most common symptoms which are associated with COVID from the beginning are Loss of taste and smell. According to the team led by researchers at the National Institutes of Health and the University of North Carolina at Chapel Hill suggested that saliva might play a role of transmitting the virus to the digestive system from the infected oral cells.

The relationship between Loss of taste and presence of Virus in the saliva has been proved when the team collected saliva from 35 volunteers who are asymptomatic or with mild symptoms. It was found that 27 out of 35 showed loss of taste and smell, which suggests that oral symptoms are most likely the result of Oral infection due to COVID-19.

The Researchers have mentioned that saliva contains high levels of SARS-CoV-2, which makes testing saliva as reliable as deep nasal swabbing. The Virus is found in saliva of both types of patients – with respiratory symptoms and without respiratory symptoms.

The study, published online March, 25, 2021 in Nature Medicine, was led by Blake M. Warner, D.D.S., Ph.D., M.P.H., assistant clinical investigator and chief of NIDCR’s Salivary Disorders Unit, and Kevin M. Byrd, D.D.S., Ph.D., at the time an assistant professor in the Adams School of Dentistry at the University of North Carolina at Chapel Hill. Byrd is now an Anthony R. Volpe Research Scholar at the American Dental Association Science and Research Institute. Ni Huang, Ph.D., of the Wellcome Sanger Institute in Cambridge, U.K., and Paola Perez, Ph.D., of NIDCR, were co-first authors.

Coronavirus requires two “Entry proteins” – ACE2 Receptors and TMPRSS2 enzyme to enter into a cell. These two Entry proteins have been found in the salivary glands and also in the lining of the oral cavity. In certain gingival cells and a small portion of the salivary gland have both the ACE2 and TMPRSS2 enzyme in the same cell, making them vulnerable to the virus and giving access to the virus.

To Confirm the findings, they collected samples from oral tissues and salivary glands in patients who had died from COVID-19 and found that more than half the samples had the SARS-CoC-2 RNA present. In salivary gland tissue from one of the people who had died, as well as from a living person with acute COVID-19, the scientists detected specific sequences of viral RNA that indicated cells were actively making new copies of the virus — further bolstering the evidence for infection.

To find out whether the infected saliva form a COVID-19 positive person can transmit the disease, researchers collected saliva from 8 asymptomatic COVID-19 patients and exposed them to healthy cells grown in a dish and found that saliva from two infected persons has transmitted the infection to healthy cells. This confirms that saliva can be a mode of transmission from even an Asymptomatic carrier to a healthy individual.