French researchers have discovered that influenza disrupts the balance of intestinal flora, thereby weakening pulmonary immune defenses and increasing the likelihood of bacterial superinfections.
Each winter, millions of French people catch the flu. Despite vaccination campaigns and treatment, the most vulnerable can develop complications which at times prove fatal. These severe forms are generally linked to pneumonia caused by bacterial superinfections. A recent study published in a prestigious journal suggests that the gut microbiota is involved.
Imbalance of intestinal flora
It is now accepted that the intestinal flora plays a key role in the proper functioning of the immune system. In this study, flu-infected mice showed a transitory imbalance in the composition and activity of their gut microbiota ( (sidenote:
Dysbiosis
Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors.
Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.)). In addition, the production of short-chain fatty acids ( (sidenote:
SCFAs
Short Chain Fatty Acids are a source of energy (fuel) for the cells of the individual. They interact with the immune system and are involved in the communication between the intestine and the brain.
Sources:
Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25.
)) was greatly reduced. SCFAs, and especially acetate, have the ability to act at a distance from the intestines on certain immune cells in the lungs (macrophages) by stimulating their antibacterial activity. In short, a dysbiosis of intestinal microbiota associated with flu is thought to reduce acetate production, compromising the lungs’ immune defenses against bacteria.
The role of diet
This intestinal imbalance is not caused directly by the virus itself, but instead seems to be the result of a reduction in food intake due to loss of appetite, a frequent flu symptom. Accordingly, in order to preserve the integrity of intestinal microbiota and strengthen immune defenses, it is recommended to consume foods that are rich in dietary fiber (e.g. vegetables, fruits and pulses). Similarly, reducing calorie intake or fasting are strongly advised against during flu outbreaks.
New therapeutic strategies
It has been shown in mice that this susceptibility to bacterial superinfection can be corrected by acetate treatment. Based on these findings, a treatment based on acetate or similar compounds is a potentially valuable therapeutic approach. Furthermore, therapeutic strategies based on the use of prebiotics and probiotics should be assessed.
Sources:
Sencio V, Barthelemy A, Tavares LP, et al. Gut Dysbiosis during Influenza Contributes to Pulmonary Pneumococcal Superinfection through Altered Short-Chain Fatty Acid Production. Cell Rep. 2020;30(9):2934–2947.e6.
