Why do some people develop severe COVID symptoms from the novel coronavirus?

The nasal microbiota contains clues about who will develop symptoms of COVID from the novel coronavirus.

The microbiota of the nose and upper throat probably contains biomarkers to assess the disease of an individual infected with SARS-CoV-2 can obtain and to develop new treatment strategies to improve their results, according to the researchers.

This nasopharyngeal microbiota is generally considered a first-line protection against viruses, bacteria and other pathogens that enter these natural passageways, says Dr. Sadanand Fulzele, a geriatric researcher in the Department of Medicine at the Medical College of Georgia in the United States. ‘University of Augusta.

Distinct patterns emerged when the researchers examined the microbiota of 27 people aged 49 to 78 who were negative for the virus, 30 who were positive but had no symptoms, and 27 who were positive with moderate symptoms who did not. did not require hospitalization, they report in the newspaper Diagnostic.

“Millions of people are infected and relatively few of them become symptomatic. This could be one of the reasons, ”says Dr. Ravindra Kolhe, director of the Georgia Esoteric and Molecular Laboratory at MCG, or GEM Lab. who performed more than 100,000 COVID tests.

Dr. Sadanand Fulzele (left) and Dr. Ravindra Kolhé. Credit: Michael Holahan, Augusta University

The most significant changes occurred in those who were symptomatic, including about half of the patients who did not have enough microbiota to even sequence, says corresponding author Fulzele.

They were surprised to find these “low readings” of bacteria in the nasopharyngeal cavity of symptomatic individuals compared to only two and four individuals in the negative and positive groups without symptoms, respectively. The vast majority of positive individuals without symptoms still had sufficient microbiota, notes first author Kolhe.

“We don’t know what happened first, the disease or the erosion of the microbiota,” says Fulzele. The runny nose and sneezing could explain the loss, an already significantly lower number of bacterial inhabitants could have increased individuals’ risk of developing these kinds of symptoms, or the virus may have changed the landscape, says Fulzele, who suspects that it is the latter.

Based on his experience with the microbiota in the gastrointestinal tract, Kolhe believes that the different content and size of the microbiota is another good bet and they both would like a definitive answer. “We don’t have enough data at the moment,” says Kolhe.

They also found differences in the type of bacteria, although the researchers note that the function of some of the bacteria they found is not well understood.

As the name of the virus and almost two years of experience with it indicate, a major method of transmission of Severe Acute Respiratory Syndrome Coronavirus 2, or SARS-Cov-2, is when a person coughs, sneezes. or even speaks, and droplets called aerosols carrying the virus travel through the air and into another person’s nose or mouth.

People aged 65 and over and / or with underlying health conditions like hypertension and diabetes are considered to be at increased risk of hospitalization and death from the infection. older individuals.

The moist, mucus-producing lining of this area works as a natural barrier against invaders and there is also a significant complement of immune cells present, Fulzele says, and their response to respiratory viruses is key.

The area is also teeming with ACE-2 receptors, which the spiny virus binds to, and Kolhe says it’s a major landing point for this virus.

Their new findings indicate that the altered microbiota in symptomatic patients impacted their immune response to the virus, according to Kolhe and Fulzele.

Symptomatic individuals had significantly higher levels of two bacterial species, including Cutibacterium, commonly found on the skin and associated with acne but also heart infections and shoulder infections following surgery. Conversely, there was a significantly lower presence of a handful of other poorly studied bacteria.

The microbiota from both infected groups, symptomatic and asymptomatic, exhibited high levels of bacteria like cyanobacteria, also known as blue-green algae, which can be found in contaminated water but is a habitual inhabitant of the microbiome in humans. man who seems to have a regulatory role. the immune response. These bacteria usually enter the body through mucous surfaces, such as those in the nose, and are known to cause pneumonia and liver damage. Those who were symptomatic had twice as much of this bacteria as their asymptomatic counterparts.

Fulzele notes that between the asymptomatic and symptomatic, there was no significant change in microbiota diversity – just these big differences in volume – but they saw a lot of individual bacteria go up and down in number.

For example, their graph of the number of another hydrophilic bacteria, Amylibacter, looked like stair steps as it went from negative to positive with symptoms, while there was a downward trend for a handful. other bacteria.

While the relationship between the nasopharyngeal microbiota and the severity of COVID-19[feminine reste inconnue, leur étude indique une “forte association” entre le microbiote nasal, l’infection par le SRAS-CoV-2 et la gravité, écrivent-ils.

Leur analyse a été effectuée avant que les variantes virales actuelles ne commencent à faire surface, mais les chercheurs affirment que les différences dans le microbiote seront probablement également valables pour celles-ci et ils ont déjà commencé cette analyse.

Des études plus importantes sont nécessaires pour s’assurer que les modèles clairs qu’ils ont trouvés se maintiennent, selon les chercheurs. Ils préparent une demande de subvention qui permettra une étude plus large et recherchent d’autres sites de test qui souhaitent être partenaires. L’utilisation du même écouvillon nasopharyngé utilisé pour de nombreux tests COVID permettrait d’effectuer une analyse du microbiote en même temps que les tests, disent-ils.

Ils notent le contraste frappant qui est apparu au cours de près de deux ans d’expérience avec le virus, la majorité des personnes infectées étant asymptomatiques ou présentant des symptômes légers comme elles le feraient avec un rhume, tandis que d’autres contractent une pneumonie virale grave, nécessitent une hospitalisation et meurent.

Une poignée d’études récentes ont maintenant été publiées suggérant que la composition bactérienne du canal nasal peut avoir une influence « drastique » sur le développement des infections respiratoires et la gravité des symptômes, écrivent-ils. Certaines études ont indiqué que le microbiote nasal peut influencer la charge virale, la réponse immunitaire et les symptômes d’une infection à rhinovirus, qui est responsable de 10 à 40 % des rhumes.

Une myriade d’autres affections comme le syndrome inflammatoire de l’intestin, les ulcères gastroduodénaux et les maladies virales ont été liées à des changements importants dans le microbiote de l’intestin, de la cavité nasale et buccale, écrivent-ils.

La diversité des bactéries dans le microbiote est généralement une bonne chose, et c’est quelque chose qui diminue naturellement avec l’âge, dit Fulzele, et peut également être altérée par des habitudes comme le tabagisme et améliorée par ceux comme une alimentation diversifiée.

Référence : « Altération du profil du microbiote nasopharyngé chez les patients âgés atteints de COVID-19 » par Ravindra Kolhe, Nikhil Shri Sahajpal, Sagar Vyavahare, Akhilesh S. Dhanani, Satish Adusumilli, Sudha Ananth, Ashis K. Mondal, G. Taylor Patterson, Sandeep Kumar , Amyn M. Rojiani, Carlos M. Isales et Sadanand Fulzele, 5 septembre 2021, Diagnostique.
DOI : 10.3390/diagnostics11091622

Le travail a été soutenu en partie par les National Institutes of Health.