Over 6,000 Americans have been hospitalized for flu so far this season. In fact, according to the Centers for Disease Control and Prevention, this season’s flu is officially classified as an epidemic. This isn’t rare—it often reaches epidemic levels, and nearly every year there are one or two fatalities. It’s not just the flu itself, however, that’s responsible. Flu opens up the body to opportunistic infections, lowering resistance and making patients more vulnerable to invading bacteria. Most of the people who died in the Spanish flu epidemic in 1918 to 1920, in fact, were victims of these infections, including pneumonia.
Scientists now think they have an idea of the mechanism behind this enhanced vulnerability to infection. What they found is that the flu virus itself alters the way the immune system works—with a little help from a molecule on the inside—and inhibits it in doing its job of protecting the body. The virus doesn’t merely protect itself, it protects attacking bacteria that are present at the same time.
The culprit, according to a German study, is a molecule called TLR7. A receptor protein, its ordinary function in healthy people is to detect and identify pathogens, microorganisms that cause disease. However, when flu strikes, TLR7 makes it harder for bacteria to be caught, and the immune foot-soldiers tasked with destroying bacteria are restrained.
Our results confirm that in the long run the flu virus suppresses the body’s ability to defend itself against bacteria. Presumably, this is an unwanted side effect of the viral infection, said Dr. Sabine Stegemann-Koniszewski, the primary author of the study, in a statement.
TLR7 can itself be suppressed. In some conditions, a drug called imiquimod is used to do just that. However, this may not work for flu because the molecule is an inherent part of the immune response to that illness. TLR7 is in fact activated by flu, and is necessary to fight that off. However, further research may find a way to make it possible to mitigate this effect while still leaving it useful against flu itself, slowing bacterial infections and making them more treatable and less common.