Khaberni - A new study has provided an explanation for why long COVID leads to neurological symptoms such as brain fog, fatigue, and mood swings, while influenza is mostly linked to respiratory complications.
Dr. Xiuwei Ben Chen, Professor of Microbiology and Immunology at the Tulane Center for Biomedical Research and the lead author of the study, said: "Influenza and COVID-19 affect large populations around the world and cause significant health damage, but the underlying mechanisms behind their long-term effects are still not fully understood."
To distinguish the shared effects of acute respiratory infections from those unique to COVID-19, researchers used a mouse model to examine lung and brain tissue after infection had subsided.
Both viruses left a similar picture in the lungs: immune cells failed to completely return to their normal state, and there was an increased accumulation of collagen (a protein associated with scarring).
These changes can increase the stiffness of lung tissue and make breathing more difficult, which may biologically explain why some people suffer from persistent shortness of breath after respiratory infections.
However, upon closer examination, researchers found a fundamental difference. After influenza, the lungs entered "repair mode," where specialized cells were sent to damaged areas to help rebuild the lining of the airways. This reparative response was largely absent after a COVID-19 infection, suggesting that the virus may interfere with the natural healing process of the lungs.
The Unique Signature of COVID in the Brain
The most clear distinctions appeared in the brain. Although neither virus was found in brain tissue, mice infected with COVID-19 showed signs of ongoing brain inflammation for weeks, alongside areas of micro-bleeding.
Gene expression analysis revealed ongoing inflammatory signals and disruptions in pathways associated with serotonin and dopamine regulation, both of which are closely linked to mood, cognition, and energy levels. These persistent changes were largely absent in animals infected with influenza.
Chen said: "In both infections, we observed long-lasting lung injury, but the long-term effects on the brain were unique to the SARS-CoV-2 virus. This distinction is fundamental to understanding long COVID."
Researchers believe the difference may be due to the nature of the immune response to each virus, where COVID-19 stimulates a prolonged inflammatory response that affects the small blood vessels in the brain, while the body's response to influenza remains more localized to the respiratory system.
By identifying these biological changes, the study provides a clearer basis for monitoring patients and developing treatments aimed at preventing long-term damage.
As the complexity of ongoing symptoms continues for some in the recovery process, understanding their causes is essential for minimizing long-term health consequences.
