If you had the flu this season, your body may have recovered—but, what about your brain? Until recently, research has been focused on the devastating--and sometimes deadly--effects of influenza on individuals with compromised immune systems, chronic illnesses, the very young and the very old. However, results published in the Journal of Neuroscience detailing the findings of a recent mouse study headed by biologist Martin Korte and his colleagues from Germany’s Technische Universität Braunschweig indicated that the flu can actually cause surprisingly negative and long-lasting effects on the brain.
In its February article on the subject, ScienceDaily’s website summarized Korte’s research: “Female mice infected with two different strains of the flu exhibit changes to the structure and function of the hippocampus that persist for one month after infection.”
While the flu is recognized as a respiratory disease, connections to neurological indicators had been made in the past, but its lasting influence on the brain had not yet been examined.
In her February article for the online edition of Newsweek, science writer Kate Sheridan explained Korte’s experiment. “For this study, mice were infected with a strain of the flu and put in something called a Morris water maze,” she wrote. “Each time the mice go into the maze, they swim around until they touch the platform.”
Following such cues as colored markers and letters in the water, Korte surmised that it would only take the mice a few swim attempts to successfully remember the location of the platform, “unless they have memory problems [resulting from influenza]”.
Over a six-month period, “mice infected with the flu went through this test four times . . . and for at least two months, they took far longer than expected to find the platform,” Sheridan wrote of Korte’s experiment. “The test was done at 30, 60, 90 and 120 days after infection.”
Korte was able to confirm that based on the performances of the infected mice, they had completely recovered their brain functions after 120 days. And while the good news is that they do recoup their cognitive capabilities, Korte pointed out that “one has to keep in mind that 120 days for the lifespan of a mouse would be equivalent to many years in humans.” Thus, recovering mental health and acuity in humans may actually require a much longer period of time.
Korte reasoned that brain inflammation is the likely cause of the maze difficulties. “This change may be happening because the brain’s version of an immune system continues to be triggered long after the sniffles subside,” Sheridan added. The inflammation results from the responses of two types of cells in the brain—the astrocytes and microglia, she explained.
“The inflammatory response in the brain holds on much longer than the actual virus is around,” Korte said.
Although this may not be the first research into how infections affect the brain, it does underline the importance of further investigation. “We would like to know if we protect the mice with the same antidotes we are using [like Tamiflu] if they are also protected from the neurological effects,” Sheridan quoted Korte.
Sheridan interviewed Richard Smeyne, a neuroscientist at Philadelphia’s Thomas Jefferson University for his opinion of Korte’s findings. “Smeyne said he was particularly concerned by the effects of the H3N2 virus, given that it is a virus strain we see often in humans,” she wrote.
According to Smeyne, further studies are already taking place. “In animal studies . . . mice that were vaccinated against the flu didn’t have this kind of immune response in their brains if they did get the virus,” he explained. “That might mean that getting a flu shot might be even more important than we realize.”
In a 2014 article for the U.S. National Library of Medicine National Institutes of Health, scientist Steven S. Coughlin, Ph.D. wrote about similar investigations into the link between mental wellness and the flu.
Like Korte, Coughlin recognized that while “accounts of mental health and infectious diseases date to antiquity . . . scientific appreciation for the many complex linkages between common anxiety and mood disorders and viral infectious diseases has rapidly expanded only in recent decades.”
Furthermore, Coughlin explained that the studies summarized in his review “indicate that there are important linkages between anxiety and depression and viral diseases such as influenza A (H1N1) and other influenza viruses.” And his conclusion, four years ahead of Korte’s investigations, is no less similar. “Additional studies are needed to further clarify the . . . interactions between mental health and communicable diseases,” he wrote, “in order to assist patients and further prevention and control efforts.”
Coughlin, S.S., Ph.D., (September 26, 2014). National Center for Biotechnology Information, U.S. National Library of Medicine. Anxiety and Depression: Linkages with Viral Diseases. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4175921/
Hosseini, S., Wilk, E., Michaelsen-Preusse, K., Gerhauser, I., Baumgärtner, W., Robert Geffers, R., Schughart, K., & Korte, M., (February 27, 2018). JNeurosci., The Journal of Neuroscience. Long-term neuroinflammation induced by influenza A virus infection and the impact on hippocampal neuron morphology and function. http://www.jneurosci.org/content/early/2018/02/28/JNEUROSCI.1740-17.2018
ScienceDaily.com. (February 26, 2018). Flu may impact brain health. https://www.sciencedaily.com/releases/2018/02/180226131447.htm
Sheridan, K., (February 27, 2018). Newsweek. Does the flue affect your mind? Bad memory and brain changes could result after the viral infection. http://www.newsweek.com/does-flu-affect-your-mind-bad-memory-and-brain-changes-could-result-after-821097