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*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

In a recent study posted to the medRxiv* preprint server, thyroxine baisse researchers at the University of North Carolina and the National Institutes of Health determined the associations between oral severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), oral antibodies against SARS-CoV-2, and coronavirus disease 2019 (COVID-19) symptoms.

Study: Oral SARS-CoV-2 host responses predict the early COVID-19 disease course. Image Credit: Kittyfly / Shutterstock


SARS-CoV-2, the causative agent of COVID-19, replicates in the upper respiratory tract, oral mucosa, salivary glands, and respiratory mucosa. The presence of angiotensin-converting enzyme 2 (ACE2) receptors and the detection of SARS-CoV-2 ribonucleic acid (RNA) and virulent SARS-CoV-2 in the oral cavity indicates that SARS-CoV-2 proliferates in the oral cavity. While lateral flow assay (LFA)-determined anti-SARS-CoV-2 responses in the oral cavity denote systemic immunity, oral biomarkers as indicators of COVID-19 prognosis have not been explored significantly.

About the study

In the present study, researchers assessed SARS-CoV-2 detection and humoral immune responses of the host in the oral cavity.

Throat wash and saliva samples were obtained from 47 symptomatic (n=17) and asymptomatic (n=30) individuals, for whom COVID-19 diagnosis was confirmed using quantitative reverse-transcription polymerase chain reaction (RT-qPCR) by analyzing nasopharyngeal (NP) swabs. In the asymptomatic group, 15 individuals showed SARS-CoV-2 seropositivity, and the remaining were seronegative or uninfected. SARS-CoV-2 nucleocapsid (N) protein was detected using immunoblot assays.

Quantitative reverse-transcription-polymerase chain reaction targeting SARS-CoV-2 subgenomic ribonucleic acid (sgRNA) sequences were confirmed by Sanger sequencing, and LFA was performed to determine anti-SARS-CoV-2 spike (S) protein receptor-binding domain (RBD) immunoglobulin G (IgG) and IgM titers. In addition, structural analysis was performed to identify molecules in the host's saliva similar to the SARS-CoV-2 nucleocapsid antigen.

COVID-19 severity was classified using the national institute of health (NIH) coronavirus disease 2019 treatment guidelines. Complete-length subgenomic polymerase chain reaction products coding for SARS-CoV-2 spike, nucleocapsid, envelope (E), or membrane (M) glycoproteins were generated from SARS-CoV-2-positive total ribonucleic acid content in saliva. Complementary deoxyribonucleic acid (cDNA) was transfected to human normal oral keratinocytes (NOK), and 48 hours post-transfection, immunoblot analysis was performed.

The crystal structure of the SARS-CoV-2 nucleocapsid antigen N-terminal ribonucleic acid-binding domain was comparatively assessed with publicly accessible structures uploaded in the molecular modeling database (MMDB). Oral cavity samples comprising greater than 10.0 RNA copies per RT-qPCR reaction were considered SARS-CoV-2-positive. COVID-19 symptoms, including muscle pain, weakness, anosmia, nausea, ageusia, upper respiratory tract symptoms, breathlessness, cough, nasal congestion, sore throat, and discharge from the nasal cavity, were assessed.


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The average age of the study participants was 40 years, with even gender distribution. At study initiation, immunoblotting analysis confirmed LFA-detected SARS-CoV-2 N antigen presence in 82.0% of the throat washes. However, only three and 17 saliva samples and throat washes, respectively, were SARS-CoV-2-positive by RT-PCR. After four weeks, 60.0% and 83.0% of saliva samples and throat washes, respectively, showed persistent SARS-CoV-2 nucleocapsid antigen presence.

SARS-CoV-2 nucleocapsid antigen lateral flow assay signal among three SARS-CoV-2-negative individuals indicated probable cross-identification of four structurally similar salivary ribonucleic acid-binding protein molecules [alignment 19 to 29 amino acid, root mean square deviation (RMSD) 1.0 to 1.5 Å]. At study initiation, symptomatic patients showed proliferation-related subgenomic ribonucleic acid junctions, and IgG titers (94% and 100% of saliva samples and throat washes, respectively) and IgM titers (75% and 63% of saliva samples and throat washes, respectively).  

At four weeks, anti-SARS-CoV-2 immunoglobulin G titers persisted in 100% of saliva samples and 83% of throat washes, and anti-IgM titers persisted in 80% of saliva samples and 67% of throat washes. Oral anti-SARS-CoV-2 IgG titers showed a 100% correlation with the nasopharyngeal swab-analyzed RT-qPCR results. The severity of fatigue and cough and the presence of weakness, nausea, and upper respiratory tract symptoms were inversely related to oral immunoglobulin IgM anti-SARS-CoV-2 titers, which were more significant among women than men. Longitudinal evaluation of symptomatic COVID-19 patients indicated oral SARS-CoV-2 persistence. COVID-19 symptoms and severity correlated with oral anti-SARS-CoV-2 antibody titers and SARS-CoV-2 presence.

The findings provide new insights into the oral biomarkers of COVID-19 prognosis, SARS-CoV-2 transmission and persistence. SARS-CoV-2 presence was detected in oral fluids from nasopharyngeal swab-analyzed RT-qPCR-positive individuals using multiple RT-qPCR-based methods of detection including (i) three distinctive pairs of primers targeting the spike-, open-reading frame 3a (ORF3a)-, or nucleocapsid-coding regions of the SARS-CoV-2 genome; (ii) ribonucleic acid copy numbers in absolute terms; and (iii) subgenomic ribonucleic acid, a biomarker of active SARS-CoV-2 replication in the initial period of symptomatic SARS-CoV-2 infection.

Overall, the study findings showed that critical for SARS-CoV-2 transmission and the course of COVID-19, SARS-CoV-2 proliferation and persistence in the oral cavity demonstrated clear associations with particular COVID-19 symptoms, early immunoglobulin titers, and participant gender during initial infection. Nucleocapsid antigen cross-reactivity might represent mimicry of structurally similar host cell proteins.

*Important notice: medRxiv 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.

Journal reference:
  • Preliminary scientific report. Oral SARS-CoV-2 host responses predict the early COVID-19 disease course, DOI:,

Posted in: Medical Research News | Disease/Infection News

Tags: ACE2, Amino Acid, Angiotensin, Angiotensin-Converting Enzyme 2, Anosmia, Antibodies, Antibody, Antigen, Assay, Biomarker, Cell, Coronavirus, Coronavirus Disease COVID-19, Cough, Enzyme, Fatigue, Genome, immunity, Immunoglobulin, Membrane, Muscle, Nasal Congestion, Nasopharyngeal, Nausea, Pain, Polymerase, Polymerase Chain Reaction, Proliferation, Protein, Receptor, Respiratory, Ribonucleic Acid, RNA, Sanger sequencing, SARS-CoV-2, Severe Acute Respiratory, Severe Acute Respiratory Syndrome, Sore Throat, Syndrome, Throat, Transcription, Transfection

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Pooja Toshniwal Paharia

Dr. based clinical-radiological diagnosis and management of oral lesions and conditions and associated maxillofacial disorders.

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