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Cigarette smoke alters microbiota and increases flu severity
Last reviewed: 02.07.2025
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A new study has found that cigarette smoke may cause disturbances in the oropharyngeal microbiota that worsen the severity of influenza A virus infection. The study is published in the journal mSystems.
Scientists have long known that cigarette smoke is harmful to health and is linked to a variety of respiratory diseases. It contributes to chronic obstructive pulmonary disease and is associated with an increased risk of influenza-related illnesses.
Recently, scientists have also shown that cigarette smoke causes disruption of the oropharyngeal microbiota, but the significance of these changes has remained unclear. The oropharynx includes the soft palate, the sides and back of the throat, the tonsils, and the back of the tongue.
Study design
In a new study, researchers showed that chronic cigarette smoke exposure alters the gut and oropharyngeal microbiota in mice. To disentangle the effects of smoking itself from the disrupted microbiota, mice were exposed to cigarette smoke and then housed smoke-exposed mice and normal-air-breathing control mice with mice that initially lacked microbiota (sterile mice). This allowed the microbiota to be transferred from the “donors” to the sterile mice.
Germ-free mice were colonized with bacteria from either smoke-exposed mice or control mice. These mice were then infected with influenza A virus and the progress of the disease was monitored.
Key Results
The researchers found that germ-free mice that acquired bacteria from smoke-exposed mice had a more severe illness, as reflected in greater weight loss. They also found that the viral infection caused significant changes in the composition of the oropharyngeal microbiota, especially on days four and eight after infection.
This study design allowed us to separate the influence of disrupted microbiota from the immunomodulatory effects of direct exposure to cigarette smoke.
Conclusion
"It is not only smoking itself that influences respiratory diseases. Our data indicate that the smoker's microbiota can also influence respiratory diseases and/or infections. In our case, this influences viral infection," said lead study author Markus Hilti, PhD, associate professor at the Institute of Infectious Diseases, University of Bern, Switzerland. "Cigarette-induced microbiota disruption is likely an important factor to consider in viral infections."