Researchers have now revealed that influenza infections can lead to an increased risk of bacterial pneumonia, which claims many lives around the world every year.
Using an animal model, the study, published in the journal PNAS found that different nutrients and antioxidants, such as vitamin C and other normally cell-protective substances leak from the blood, thereby creating an environment in the lungs that favours the growth of the bacteria.
The bacteria adapt to the inflammatory environment by increasing the production of the bacterial enzyme HtrA.
The presence of HtrA weakens the immune system and promotes bacterial growth in the influenza-infected airways. The lack of HtrA stops bacterial growth.
“The ability of pneumococcus to grow in the lower airways during an influenza infection seems to depend on the nutrient-rich environment with its higher levels of antioxidants that occurs during a viral infection, as well as on the bacteria’s ability to adapt to the environment and protect itself from being eradicated by the immune system,” said study author Birgitta Henriques Normark from Karolinska Institutet in Sweden.
The results provide valuable information on how bacteria integrate with their environment in the lungs and could be used to find new therapies for double infections between the influenza virus and pneumococcal bacteria.
“HtrA is an enzyme, a protease, which helps to weaken the immune system and allows pneumococcal bacteria to penetrate the protective cell layer on the inside of the airways,” said study author Vicky Sender.
“A possible strategy can therefore be the use of protease inhibitors to prevent pneumococcal growth in the lungs,” Sender added.
It is still not known if Covid-19 patients are also sensitive to such secondary bacterial infections, but the researchers think that similar mechanisms could potentially be found in severely ill Covid-19 patients.
“It’s likely that acute lung inflammation, regardless of cause, gives rise to leakage of nutrients and antioxidants, and to an environment that fosters bacterial growth,” Henriques Normark noted.