Smoking has long been known as unhealthy. It is known to lead to chronic pulmonary disease and has also been associated with increased risk for influenza-related illness, among a host of other conditions.

More recently, scientists demonstrated a link between cigarette smoke and a disordering of the oropharyngeal microbiota composition. However, this association has not been clear. The soft palate, side and back walls of the throat, tonsils, and the back of the tongue make up the oropharynx.

To decode, researchers from the University of Bern, Bern, Switzerland led a mice study.

They showed that gut and oropharyngeal microbiota are altered by chronic cigarette exposure in mice.

Markus Hilty, Associate Professor at the Institute for Infectious Diseases, at the varsity said that smoking alone does not impact respiratory disease.

“The smoker’s microbiota may also impact respiratory disease and/or infection. In our case, it impacts viral infection,” said Hilty.

In the study, the team exposed mice to cigarette smoke, and then cohoused them with air-exposed mice (control) and germ-free mice.

The experiment allowed the transfer of the microbiota from donor mice to germ-free mice.

The results, published in mSystems, a journal of the American Society for Microbiology, showed that the original germ-free mice were colonised either with bacteria from a smoke-exposed or air-exposed mouse.

Further, the team infected the recipient mice with influenza A virus and monitored the disease course.

They found that the original germ-free mice who received bacteria from smoke-exposed mice had a more severe disease course, which was measured by increased weight loss.

In addition, virus infection was linked with substantial changes in the oropharyngeal microbiota composition. The changes were particularly visible on day 4 and day 8 after infection.

Hilty urged physicians to consider “cigarette-induced disordering of the microbiota as probably an important factor during viral infection”.