Taste receptors located on the human tongue have an angiotensin-converting enzyme that serves as a pathway for SARS-CoV-2 to enter the body’s cells.
Researchers from the U.S. National Institute explained why COVID-19 patients experience changes in smell or taste.
The relevant scientific paper is published on bioRxiv.
Scientists found that the taste buds located on the human tongue have angiotensin-converting enzyme 2 (ACE2). Through this fragment, the SARS-CoV-2 virus enters the cells of the body. Thus, when infected with coronavirus, taste is affected.
Josephine Egan, the study lead author with his team studied thousands of human taste buds.
The researchers write:
“By demonstrating the co-localization of SARS-CoV-2 virus, Type II taste cell marker, and the viral receptor ACE2, we show evidence for replication of this virus within taste buds that could account for acute taste changes during active COVID-19. This work also shows that the proliferation of the taste stem cells in recovering patients may take weeks to return to their pre-COVID-19 state, providing a hypothesis for more chronic disruption of taste sensation, reports of which are now appearing in the medical literature.”
For their research, researchers took samples of the fungiform pallipae — with one region containing taste buds — in a 45-year-old woman with controlled hypertension and who had presented with SARS-CoV-2. During her course of infection, she reported changes in her sense of taste, including not being able to taste the sweetness from chocolate and describing curry as ‘white.’
Her tongue was physically enlarged and redder around the fusiform pallipae than in a separate examination three months before.
The team confirmed the presence of SARS-CoV-2 RNA in the fusiform pallipae area, specifically in PLCB2 positive cells. The virus was also found in the lamina propria with disruptions in the stem cell layer. Six weeks after symptoms improved, which coincided with the patient’s recovery of sense of taste.
Another patient was a 63-year-old man with no preexisting conditions who had donated samples of his fusiform pallipae in 2019 before the pandemic. More samples were taken six weeks after he tested positive for COVID-19 infection. Though he experienced several long COVID symptoms, including mild loss of taste — coffee tasted like mud, and he could not taste chocolate. Samples of his fusiform pallipae 10 weeks after infection showed no presence of the virus. However, compared to his 2019 samples, he had altered changes to the stem cell layer of the tongue.
Based on the results, the researchers suggest impairments in stem cells may affect turnover and could contribute to the delayed recovery of sense of taste.
*Important Notice
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.