New research used a mouse model to compare tissue after infection had cleared and to distinguish effects common to severe respiratory infections from those unique to SARS‑CoV‑2. The study examined lungs and brains to identify lasting changes after COVID‑19 and after influenza.
In the lungs, both viruses left similar signs of persistent injury. Investigators observed immune cells that failed to fully stand down and an increased buildup of collagen, a protein associated with scarring. Collagen accumulation and unresolved inflammation can stiffen lung tissue and help explain lingering shortness of breath after respiratory infection. After influenza, a clear repair response emerged: specialized cells appeared in damaged areas and began to rebuild the airway lining. That repair response was largely absent following COVID‑19 infection.
Differences were most striking in the brain. Neither virus was detected in brain tissue, yet mice that had COVID‑19 showed persistent brain inflammation weeks later and tiny areas of bleeding. Gene expression analysis revealed ongoing inflammatory signaling and disruption of pathways that regulate serotonin and dopamine, systems related to mood, thinking and energy. Those persistent molecular and vascular changes were largely absent in influenza‑infected animals.
- Brain fog
- Fatigue
- Mood changes
The authors say these vascular and immune changes may contribute to lasting neurological symptoms, while influenza is more often linked to respiratory complications. The research aims to provide a firmer foundation for patient monitoring and for developing treatments to prevent lasting damage. Support came from the American Heart Association Long COVID Impact Project, the National Institutes of Health and institutional funding.
Difficult words
- persistent — continuing for a long time, not going away
- collagen — a structural protein in connective tissue
- inflammation — body's protective response causing redness or swelling
- vascular — relating to blood vessels in the body
- gene expression — process by which a gene makes its product
- serotonin — a brain chemical that affects mood and sleep
- dopamine — a brain chemical linked to motivation and reward
- repair — process of fixing damaged tissue or structures
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- The study found lasting brain inflammation after COVID‑19 in mice. How might this finding affect how patients recovering from COVID‑19 are monitored?
- Why could the absence of a clear repair response in the lungs after COVID‑19 be important for patients compared with influenza?
- What kinds of treatments or research would you suggest to prevent lasting neurological damage after respiratory infections, and why?
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