Dangerous cocktail: flu and pneumonia

Dr. Andrea Bannert has been with since 2013. The doctor of biology and medicine editor initially carried out research in microbiology and is the team's expert on the tiny things: bacteria, viruses, molecules and genes. She also works as a freelancer for Bayerischer Rundfunk and various science magazines and writes fantasy novels and children's stories.

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Those who have caught the flu are particularly at risk for pneumonia. The two responsible pathogens - influenza virus and pneumococcus - can be fatal in combination. The reason apparently lies in the immune system.

The flu virus sloshes through Germany in regular waves of illness and kills itself every year. A large proportion of patients who die as a result of the flu have also become infected with bacteria that cause pneumonia.

Double infections are more aggressive

Most of them are stems from Streptococcus pneumoniae, the so-called pneumococci. Many of these tribes are harmless. For example, they colonize the nasopharynx and hardly cause any symptoms. This is different in combination with influenza viruses: the double infection seems to make the bacteria more aggressive.

A team of scientists led by Dunja Bruder from the Helmholtz Center for Infection Research in Braunschweig examined this connection in more detail. The researchers infected mice with influenza viruses and at the same time with pneumococcal strains of different danger. They injected either only the influenza viruses or only pneumococci into a control group of animals.

The result: In the double-infected animals, the bacteria spread much faster in the body than in those mice that were only infected with pneumococci of the same strain. This also applied to actually harmless pneumococcal strains. “We have observed that even less aggressive strains in influenza-infected mice can lead to fatal courses of the disease. Even with low bacterial doses, ”reports study co-author Sabine Stegmann-Koniszewski to

Excessive immune response

Apparently the flu-ridden rodent's immune system was no longer able to react appropriately. As a result, the bacteria multiplied very quickly. When the researchers took a closer look at the immune response, they realized that it actually differed greatly between single and double infections.

When infected with certain pneumococcal strains, the concentration of so-called neutrophils increased in the lungs. Neutrophils are specialized immune cells that fight bacteria, but can also lead to violent inflammatory reactions that attack the body's own tissue.

Curb the inflammatory reaction with medication

This finding could be important for the treatment of double infections with pneumococci and viruses: "It is often not enough to simply combine drugs against the influenza viruses and the bacteria," said Bruder. You need additional medication to prevent the immune system from overreacting.

The scientists now want to examine the behavior of different pneumococcal strains in the event of a double infection in more detail. This will make it possible to select anti-inflammatory drugs in an even more targeted manner in the future.

Source: Bruder D. and Stegemann-Koniszewski et al .: nfluenza A virus infection predisposes hosts to secondary infection with different Streptococcus pneumoniae serotypes with similar outcome but serotype-specific manifestatio

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