Micro-CT imaging reveals the effects of oseltamivir on H1N1-induced pulmonary alterations.

Introduction: Influenza A H1N1 virus infection is a major cause of viral pneumonia and may progress to severe pulmonary complications, including bronchiectasis, characterized by irreversible airway dilation and impaired mucociliary clearance. Oseltamivir (Tamiflu®) is the antiviral treatment of choice; however, its efficacy depends on early administration. Objective: To evaluate the effects of H1N1 infection and delayed oseltamivir treatment on structural and functional lung alterations in mice. Methods: Mice were infected with H1N1 virus and treated with oseltamivir after the recommended therapeutic window (48 h post-infection) to allow pneumonia establishment. Pulmonary alterations were assessed by micro-computed tomography (micro-CT), including lung weight and volume, aerated and non-aerated areas, and airway caliber. Pulmonary function was evaluated by whole-body plethysmography using enhanced pause (Penh). Results: Viral infection induced significant pulmonary alterations, evidenced by increased lung weight and volume, expansion of non-aerated areas, reduction of normally aerated regions, and opacities consistent with pulmonary inflammation. Delayed oseltamivir treatment did not reverse these changes or improve elevated Penh values. However, micro-CT analysis revealed increased airway caliber, consistent with bronchiectasis-like features, which was partially attenuated by oseltamivir at 30 mg/kg. Conclusion: Influenza H1N1 infection induces marked structural and functional pulmonary alterations after seven days, including features consistent with bronchiectasis. Although delayed oseltamivir treatment showed limited efficacy against established inflammation and respiratory dysfunction, it partially reduced airway dilation, suggesting a protective effect against virus-induced tissue damage. These findings reinforce the importance of early intervention in influenza and improve understanding of antiviral effects at different disease stages.