SARS-CoV-2 infection of the oral cavity and saliva
The study titled “SARS-CoV-2 infection of the oral cavity and saliva” provides crucial insights into the role of the oral cavity in COVID-19 infection and transmission.
Here’s a detailed summary:
Background: Despite common oral symptoms in COVID-19, like taste loss, dry mouth, and mucosal lesions, the involvement of the oral cavity in COVID-19 has been poorly understood. This study aimed to address this gap by examining the human minor salivary glands and gingiva for signs of SARS-CoV-2 infection.
Methodology: The study utilized two single-cell RNA sequencing datasets of the human minor salivary glands and gingiva, comprising 9 samples and 13,824 cells. This analysis identified 50 cell clusters and classified 34 unique cell subpopulations between the glands and gingiva. Researchers focused on identifying SARS-CoV-2 viral entry factors, such as ACE2 and TMPRSS members, in these tissues.
- Viral Tropism Prediction: The study predicted the viral tropism of SARS-CoV-2 and other coronaviruses by analyzing cell-specific susceptibilities. It found that viral entry factors were broadly expressed in epithelial cells of the salivary glands and oral mucosae. ACE2 and TMPRSS members were particularly enriched in these cells, suggesting a wide susceptibility to viral infection.
- Infection in Oral Tissues: Researchers confirmed SARS-CoV-2 infection in both the salivary glands and oral mucosae. They also noted that saliva from COVID-19-infected individuals contained epithelial cells exhibiting ACE2 and TMPRSS expression, indicating sustained infection. This finding was significant as it suggested that the oral cavity could be an important site for SARS-CoV-2 infection and might play a role in virus transmission through saliva.
- Salivary Viral Shedding and Immune Response: The study observed distinct viral shedding dynamics in matched nasopharyngeal and saliva samples. Moreover, the salivary viral burden correlated with COVID-19 symptoms such as taste loss. Importantly, even in asymptomatic cases, sustained salivary IgG antibodies against SARS-CoV-2 were found post-recovery, indicating a prolonged immune response.
- Infection and Replication in Salivary Cells: The research demonstrated that oral mucosal epithelial cells are infected by SARS-CoV-2 and can shed the virus into saliva. This was confirmed through various techniques, including in situ hybridization (ISH) and immunohistochemistry (IHC). The study found that SARS-CoV-2 infection and replication were more frequent in the suprabasal layers of the oral mucosa. Salivary epithelial cells expressed all SARS-CoV-2 entry factors, and a subset of these cells sustained viral infection.
Conclusion: This study provides comprehensive evidence that the oral cavity, including the salivary glands and mucosae, is a significant site for SARS-CoV-2 infection and transmission. It highlights the importance of the oral route in the dynamics of COVID-19 infection and underscores the need for further research in this area, especially regarding the role of saliva in transmitting the virus.