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New study explains important cause of flu deaths

Author: Aldiyarbek Nurlan 

Translator: Tursunova Balkadisha 

Editor: Akhmetova Aigerim  



The Spanish flu was an influenza pandemic that swept the world in 1918-2020 and, unlike many other pandemics, disproportionately affected young, otherwise healthy adults. One of the important reasons for this was the so-called superinfections caused by bacteria, in particular pneumococci. 


Flu is caused by a virus, but the most common cause of death is secondary bacterial pneumonia, not the flu virus itself. Pneumococcal infections are the most common cause of community-acquired pneumonia and the leading cause of death in the world. Previously transmitted influenza virus infection increases sensitivity to pneumococcal infections, but the mechanisms underlying this increased susceptibility are not fully understood. Researchers at the Karolinska Institute have identified flu-induced changes in the lower respiratory tract that affect the growth of pneumococci in the lungs. 


Using an animal model, the researchers found that various nutrients and antioxidants, such as vitamin C and other substances that normally protect cells, seep out of the blood, thereby creating an environment in the lungs that promotes bacterial growth. 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 the growth of bacteria in the flu-infected Airways. Lack of HtrA stops the growth of bacteria. 


"The ability of pneumococcus to grow in the lower respiratory tract during influenza infection seems to depend on the nutrient-rich environment with higher levels of antioxidants that occurs during viral infection, as well as on the ability of bacteria to adapt to the environment and protect themselves from being destroyed by the immune system," says chief researcher Birgitta Henriques Normark. 


HtrA is an enzyme, a protease, that helps weaken the immune system and allows pneumococcal bacteria to enter the protective layer of cells inside the respiratory tract.