Intranasal administration of alpha interferon reduces seasonal influenza A virus morbidity in ferrets.

The type I interferon (IFN) response represents one of the first lines of defense against influenza virus infections. In this study, we assessed the protective potential of exogenous IFN-alpha against seasonal and highly pathogenic influenza viruses in ferrets. Intranasal treatment with IFN-alpha several hours before infection with the H1N1 influenza A virus strain A/USSR/90/77 reduced viral titers in nasal washes at least 100-fold compared to mock-treated controls. IFN-treated animals developed only mild and transient respiratory symptoms, and the characteristic fever peak seen in mock-treated ferrets 2 days after infection was not observed. Repeated application of IFN-alpha substantially increased the protective effect of the cytokine treatment. IFN-alpha did not increase survival after infection with the highly pathogenic H5N1 avian influenza A virus strain A/Vietnam/1203/2004. However, viral titers in nasal washes were significantly reduced at days 1 and 3 postinfection. Our study shows that intranasal application of IFN-alpha can protect ferrets from seasonal influenza viruses, which replicate mainly in the upper respiratory tract, but not from highly pathogenic influenza viruses, which also disseminate to the lung. Based on these results, a more intensive evaluation of IFN-alpha as an emergency drug against pandemic influenza A is warranted.