Does the Flu Have a Lasting Effect?

Generally, people breathe a huge sigh of relief after recovering from the flu. But according to the latest research, some strains of the flu virus can leave a lasting impression. Following infection, viruses like the H3N2 strain are shown to cause forgetfulness in mice for months after recovery. This means that as well as burdening the body with fevers, chills and aches, the flu can also trigger memory issues and minor brain damage.  

The findings were published in the Journal of Neuroscience and warm that while it's unclear if H3N2 affects humans the same way it affects mice, there is some cause for concern. It examined the side effects of three strains of influenza A - H1N1, H7N7 and H3N2. The first was the virus that triggered the 2009 swine flu outbreak, while the second is relatively dangerous but rarely infects humans. The third was once of the major culprits behind the 2017/18 flu season, which was considered particularly fierce.

Some flu strains trigger memory issues in mice

Together with a team of colleagues, neurobiologist Martin Korte of Germany's Technische Universitat Braunschweig infected groups of mice with the viruses, then looked for memory issues at 30, 60 and 120 day periods. While a month after being infected all mice showed full signs of physical recovery, those that had received the H3N2 and H7N7 injections showed clear memory issues. Meanwhile, mice that had not been infected with influenza or received the milder H1N1 strain were able to perform tasks normally.

They went on to conduct more research and found that after recovering from infection, message-receiving dendritic spines found on hippocampus nerve cells appeared to decrease significantly. Similarly, the same decline wasn't noted in test group mice, or those that were infected with the H1N1 strain.

Flu hits the hippocampus

Located within the brain's medial temporal lobe, the hippocampus is a small organ that's largely associated with memory. Korte and his team went on to conduct further electrical experiments and found that post-recovery, the signal-sending abilities of the nerve cells were compromised. Furthermore, the mice’s brains appeared to be inflamed with microglia, immune cells that were still active up to 60 days after infection.

Of course, human brains are bigger, stronger and more complex than those of mice. While Korte doesn't suggest that catching the flu can cause long-term brain damage, he does assert that “the news is more that we should not only look at lung functionality after the flu, but also cognitive effects, weeks and months after infection.”

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