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Future research will examine whether the oral microbiome and mucosal immunity could protect South Asian communities in the UK and India against SARS-CoV-2 infection. (Image: ETAJOE/Shutterstock)

COVID-19: Examining role of oral microbiome and mucosal immunity in South Asian populations

By Iveta Ramonaite, Dental Tribune International
June 28, 2021

LONDON, UK/CHENNAI, India: UK Research and Innovation and India’s Department of Biotechnology in the Ministry of Science and Technology have recently granted funding to two research projects that aim to examine the impact of COVID-19 in South Asian communities in India and the UK. One of the studies hypothesises that mucosal immunity and the oral microbiome play a critical role in susceptibility to and severity of COVID-19. If confirmed, the findings of the study could help mitigate the severity of the disease in both countries.

The first project will investigate why COVID-19 affects South Asians differently in different countries and may contribute to the development of new prevention measures, more targeted monitoring and new treatments aimed at improving the outcome of COVID-19 in India and the UK.

“It’s an extraordinary opportunity to learn how the immune systems of South Asians are confronting COVID-19 in India compared to how South Asians fared in London last year. It’s basic science that has ceaselessly brought progress throughout this tragic pandemic, and we hope that this study can continue in that vein,” lead researcher Prof. Adrian Hayday, from the School of Immunology and Microbial Sciences at King’s College London, said in a press release.

Dr Stephen J. Challacombe, Martin Rushton professor of oral medicine at King’s College London. (Image: Stephen Challacombe)

The second project is based on the hypothesis that mucosal immunity and the oral microbiome play a critical role in susceptibility to and severity of COVID-19. “There is a confirmed disparity in the susceptibility to COVID-19 in different ethnicities,” lead researcher Dr Stephen J. Challacombe, Martin Rushton professor of Oral Medicine in the Centre for Host-Microbiome Interactions at King’s College London, stated in a press release. He continued: “Increasing evidence suggests that SARS-CoV-2 actively infects the mouth. Accordingly, whether it enters the circulation, causing more severe disease, may be related to oral health.”

Challacombe believes that the oral microbiome can both protect and compromise our overall health and that it varies considerably with ethnicity. “This study proposes that immunity at mucosal sites along with the oral microbiome plays a critical role in COVID-19 susceptibility and severity, and ethnic-specific differences in both these factors explain mortality variations between similar populations in the UK and India,” he explained.

The rationale behind the study

“We have been studying mucosal immunity for many years, and particularly the role of local oral immunity in protection from, or susceptibility to, oral diseases. This included dental caries, periodontal disease, but especially candida infection and other mucosal diseases, including recurrent aphthous ulceration and other types of mouth ulcers,” Challacombe told Dental Tribune International (DTI). “Our previous work with HIV infection showed what a special fluid saliva is, and what powerful antiviral factors exist in saliva and protect us against not only HIV but also other viruses, including herpes,” he added.

“There is a confirmed disparity in the susceptibility to COVID-19 in different ethnicities”
— Dr Stephen J. Challacombe, King’s College London

Challacombe explained that COVID-19 is essentially a mucosal disease and that evidence shows that the virus replicates within the salivary glands, both major and minor. He told DTI that there are approximately 10,000 infectious viral particles in each microlitre of saliva in the early stages of infection and that about 5–10 µl of these particles are spread when licking one’s lips. Given the numbers, Challacombe believes that saliva is a high-risk fluid for transmitting SARS-CoV-2 and that dentists, anaesthetists and otolaryngology surgeons are at high risk of catching COVID-19 from their patients.

Challacombe is currently working on another study that aims to prove that using powerful antiviral agents such as povidone-iodine can help reduce the risk of SARS-CoV-2 infection for healthcare professionals. To reduce the viral count, patients ought to gargle with iodine mouthwash or use iodine sprays before dental treatment or during hospitalisation. This, in turn, should keep SARS-CoV-2 at bay for at least 30 minutes and possibly up to 2 hours, the researchers believe.

Call for research

While Challacombe was undertaking the study on iodine in Chennai in India, the Medical Research Council put out a call for research proposals for joint UK–India partnerships. The council sought to understand why South Asian populations in the UK suffered more severe consequences of SARS-CoV-2 infection compared with similar populations in India. Since Challacombe and his team were already working on their study in India, they were quick to respond to the call, he told DTI.

“Much research on the oral microflora has shown it to be protective against pathogens, including viruses, attempting to colonise the mouth. Very little research, however, has been done to determine whether the oral microbiome plays a role in protection against SARS-CoV-2 infection,” he commented. “The opportunity was thus taken to suggest that a study of both the oral microbiome and mucosal immunity would be relevant to understanding COVID-19 and this was the basis of the grant. Thus, we are comparing these factors in controls and in SARS-CoV-2 infected adults in Asian and non-Asian populations.”

“Our previous work with HIV infection showed what a special fluid saliva is”
— Dr Stephen J. Challacombe, King’s College London

Talking about the importance of the study, Challacombe explained: “If the presence of oral disease is indeed a factor in COVID-19, it will enhance the role of dentistry and appreciation of the importance of oral health to general health. If biomarkers can be identified, either in the microbiome or in the immune factors studied, this will potentially have a significant impact on the prevention of COVID-19 and the prediction of the severity of the disease.”

The first project is titled “Variation in innate immune activation and cardiovascular disease risk as drivers of COVID-19 outcome in South Asians in UK and India.”

The second project is titled “Role of the oral microbiome and mucosal immunity in COVID-19 disease: diagnostic/prognostic utility in South Asian populations.”

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