When people talk about influenza, a general focus of the conversation is the physical symptoms — fever, congestion, muscle aches, and chills. In the vast majority of flu cases, these subside within a few weeks, and the virus disappears. But if you’ve ever felt the mental fog that comes with illness linger after physical symptoms disappear, there might now be science to explain why.
A study released this week in the Journal of Neuroscience found evidence that certain strains of influenza can cause neurological changes in the brain long after the illness is gone. With research performed on mice, the study is a look at an aspect of influenza that has been largely overlooked in this current epidemic, which has killed dozens of children in the United States since October and has infected tens of thousands of people nationwide.
For this particular examination, researchers from Germany’s Braunschweig University of Technology chose to infect mice with three different strains of influenza. The first, H1N1, was the culprit in 2009’s swine flu pandemic; the second, H7N7, is a version that’s rare in humans; and the third, H3N2, is the current strain spreading through the United States.
The goal was to find out what, if any, lingering effects all three would have on the brain.
In order to measure this, researchers used the Morris Water Maze — a standardized test in which mice have to find a platform hidden below water. How quickly they find it — and which research cues they use — allows researchers to closely measure changes in spatial learning and memory. Both rely heavily on a region of the brain called the hippocampus, a center of learning, emotion, and memory.
After the mice recovered from their respective influenza strains, the researchers put their navigation skills to the test — and found obvious differences in performance based on which strain of the flu the mice had. In the first 30 days, mice infected with either H3N2 or H7N7 had more trouble locating the hidden platform — signaling neurological damage to their hippocampal region. In some of the mice, this damage persisted for 60 days. For reasons that are still unclear, no changes were recorded in the mice infected with H1N1.
One of the lead researchers on the study, Martin Korte, a neurobiologist at Braunschweig University of Technology, says it’s not unlikely that these symptoms are mirrored in humans. “In terms of single brain neurons and immune cells in the brain, humans and mice are very much alike,” Korte tells Yahoo Lifestyle. “So, overall, we believe that the cognitive defects we observed in young mice are also very relevant for humans.”
Korte says observing the mice become “slower and less precise” after the flu is significant but shouldn’t be cause for alarm. “The effect was visible and obvious, but we have by no means induced Alzheimer’s-like symptoms in young mice,” he says. “The story might be different in old mice, and also in older humans.”
Based on his research, the brain effects of the flu could last for roughly 30 days in young adults, and potentially longer in the older population. “There is some indication that in [older populations] it could lead to mild cognitive impairment that lasts,” Korte tells Yahoo Lifestyle. “As far as we can judge from preliminary experiments, the initial immune response in old mice is stronger and long-lasting.”
Further studies need to be done to deduce the larger impact in older populations, but for younger ones, Korte suggests trying to limit difficult activities in the aftermath of a flu. “In younger people, they should worry about the four to eight weeks after the infection,” Korte says. “Taking an exam, for example, might be more difficult.”
In terms of prevention, he sees an obvious solution: “Get vaccinated,” Korte tells Yahoo Lifestyle. “It appears that the strength of the initial response leads to strong neurological effects, and with a vaccination, this response is much weaker.” On top of that, he recommends hand washing and — for those who do contract the virus — taking time to fully recover at home.
To be clear, the study is not aimed at proving the flu precipitates long-term brain damage. Rather Korte hopes it will raise awareness about how the virus can affect the way our brains work — and prompt other researchers to take a closer look at this.
“We need to rethink the assumption that the brain is an immune-privileged organ,” Korte says. “And it is a stronger reminder that infection should be taken seriously — in terms of both treatment and research. The more seriously we take [it], the better our chance of success.”
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