New research highlights the unexpected role of microbiota in disease severity. Smoking has long been linked to severe respiratory conditions. Still, a new study suggests the damage may run even more profoundly than previously understood, into the microscopic ecosystem of bacteria in the throat. According to findings published in mSystems, cigarette smoke alters the oropharyngeal microbiota, increasing the severity of Flu Infections in patients.
Researchers from the University of Bern, Switzerland, have uncovered that it’s not just smoke exposure itself that leads to more severe illness. The disordered microbiota caused by smoking may also directly impact how the body responds to viral infections.
Experiment Links Microbiota Changes to Worse Flu Infections Outcomes
Scientists conducted controlled experiments on mice to separate the effects of cigarette smoke from those of the resulting microbiota changes. One group of mice was exposed to cigarette smoke, while another breathed clean air. Researchers then took germ-free mice—mice raised in sterile conditions without microbiota—and introduced microbial communities from the two groups.
Once colonized, all the germ-free mice were infected with influenza A virus. The mice that received microbiota from the smoke-exposed group experienced significantly worse illness, measured by increased weight loss and more severe symptoms. These effects occurred even though the mice had never been directly exposed to cigarette smoke.
Flu Virus Further Disrupts Microbial Balance
The researchers also observed that influenza infection led to additional shifts in oropharyngeal microbiota, particularly noticeable on days 4 and 8 after infection. This suggests a feedback loop: smoking disrupts microbiota, which worsens flu symptoms, and the virus further disturbs the microbial balance.
This discovery reveals a previously underexplored mechanism for how smoking may exacerbate respiratory illness—not through toxins alone but through a microbial imbalance in the oropharynx, which includes the soft palate, tonsils, and back of the tongue.
Implications for Public Health and Smoking Cessation
“The cigarette-induced disordering of the microbiota is probably an important factor to consider during viral infection,” said Dr. Markus Hilty, associate professor at the University of Bern’s Institute for Infectious Diseases and corresponding author. Flu Infections.
These findings highlight an additional, less visible risk of cigarette smoke. The microbial disruption it causes could have lingering effects, even after smoking stops, potentially leaving individuals more vulnerable to viral infections such as influenza.
With flu season posing a recurring threat and microbial health becoming an increasingly studied frontier, the research adds another compelling reason to avoid smoking—and raises important questions about how restoring microbial balance might play a role in treating respiratory illness.
Reference: Tsering Wüthrich, Simone de Brot, Veronica Richina, Nadja Mostacci, Zora Baumann, Nathan G. F. Leborgne, Aurélie Godel, Marco P. Alves, Mohamed Bentires-Alj, Charaf Benarafa, Markus Hilty. Cigarette smoke-induced disordered microbiota aggravates the severity of influenza A virus infection. mSystems, 2024.
