Cigarette smoke changes the microbiota and worsens the severity of the flu, researchers find

New research has shown that cigarette smoke can cause disrupted oropharyngeal microbiota, which worsens the severity of influenza A virus infection. The investigation was published in mSystems.

Researchers have long known that cigarette smoke is unhealthy and is linked to many different respiratory diseases. Cigarette smoke promotes the development of chronic lung diseases and is associated with an increased risk of flu-related illnesses.

More recently, scientists have shown that cigarette smoking is also associated with a disturbance in the composition of the oropharyngeal microbiota, but the relevance of this disturbance is not clear. The oropharynx includes the soft palate, the side and back walls of the throat, the tonsils, and the back of the tongue.

In a new study, researchers showed that the intestinal and oropharyngeal microbiota are altered by chronic cigarette exposure in mice. The researchers attempted to disentangle the effect of smoking and disrupted microbiota by exposing mice to cigarette smoke and then housing mice exposed to cigarette smoke and air-exposed mice (control) with germ-free mice. This allowed the transfer of the microbiota from donor mice to the germ-free mice.

The original germ-free mice were colonized with bacteria from a smoke- or air-exposed mouse. The scientists then infected the recipient mice with the influenza A virus and monitored the progression of the disease.

The researchers found that the original germ-free mice that received bacteria from smoke-exposed mice had a more severe course of disease, as measured by increased weight loss. Furthermore, virus infection was found to be associated with substantial changes in the composition of the oropharyngeal microbiota, especially on days four and eight after infection.

The study design made it possible to disentangle the effect of the disrupted microbiota from the immunomodulatory effects of actual cigarette smoke exposure.

“It is not just smoking itself that influences respiratory disease, but our data indicate that the smoker’s microbiota can also influence respiratory disease and/or infections. In our case, it affects viral infections,” said corresponding study author Markus Hilty, Ph. .D., associate professor at the Institute of Infectious Diseases, University of Bern in Switzerland. “The disruption of the microbiota caused by cigarettes is likely an important factor to take into account during a viral infection.”