Dangerous bacterial infections can go hand-in-hand with influenza, or the flu, yet the link between the two is largely unknown. By using mice, a team of researchers from across the globe has now uncovered a possible explanation that might point to a new form of treatment.
Despite vaccination programs, seasonal flu is a significant health concern. The Centers for Disease Control and Prevention (CDC) note that up to 61,000 flu deaths have occurred in the United States each year since 2010.
According to the same estimates, between 9 million and 45 million people have had the flu every year in a similar period.
Although most people quickly recover from the illness, some may experience complications that can prove fatal.
Bacterial superinfections, which doctors often link to bacterial pneumonia, are well-known risks that increase morbidity and mortality rates of the flu.
These infections can impact both people with preexisting respiratory conditions and those who were previously healthy. So, finding a way to stop and treat them is just as important as preventing the flu.
A new study, appearing in Cell Reports, has now delved further into whether changes to the gut microbiota influence a person’s risk of secondary bacterial lung infections.
Uncovering a mystery
Researchers from specialist laboratories and centers in France, Brazil, Scotland, and Denmark took part in the study.
The teams focused on the gut microbiota, the trillions of microbes that live in the intestines and help determine everything from immune system responses to food digestion rates.
Experts know that diet affects the way gut microbiota work, as well as their makeup. Now, the latest study suggests the flu can change the gut microbiota’s structure.
Furthermore, scientists already know that a change to the gut microbiome can play a role in the development of chronic diseases.
For the latest study, the research teams examined the effect of the flu on the gut microbiota of mice, looking to see if it resulted in a change to disease outcomes.
The results showed that not only did the influenza infection alter the function and makeup of the microbiota, it also made the mice more susceptible to bacterial superinfections of the lung.
The researchers saw weakening of the lung’s defense mechanism, particularly its ability to fight off Streptococcus pneumoniae.
The dietary link
The teams looked at how influenza infection with H1N1 and H3N2 affected the gut microbiome of mice. They saw changes in the composition and metabolic output of the microbiota.
They believe diet likely drives this relationship between flu and gut microbiota, as people with the flu tend to eat less, which can lead to changes in the microbiome.
The mice in the study also ate less, and the researchers solidified their theory by observing similar microbiota changes in these food restricted mice.
The study also links both flu and a restricted diet to a decrease in short-chain fatty acid (SCFA) production.
Treatment with acetate, which is an SCFA, protected the mice that had flu — and were later exposed to Streptococcus pneumoniae — from developing a bacterial superinfection.
The findings only showed a clear link between food intake, flu, and bacterial superinfections in mice, and it will be some time before human tests take place.
Still, the research could point the way toward a new nutritional treatment for these dangerous infections.
The study also sheds light on potential avenues for preventing bacterial pneumonia, which is one of the deadliest flu complications for many people.
Flu, however, is not the only sometimes serious illness that this approach could mitigate. The researchers suggest that sepsis, as well as bacterial infection after serious burn injuries or trauma, may benefit from this approach.