Influenza virus infection and postviral bacterial pneumonia pathogenesis induced by different subtypes of influenza virus in mice

Secondary bacterial infections after influenza virus infection further increase morbidity and mortality due to influenza. Despite of seasonal influenza vaccination, antiviral drugs and antibiotics are widely used in viral/bacterial pneumonia therapy. Therefore, further comprehensive study of the infection pathogenesis is relevant. Murine models for influenza virus infection were reproduced with different virus subtypes A/California/04/2009MA (pandemic H1N1 2009), A/Puerto Rico/8/34 (H1N1) and A/Aichi/2/69 (H3N2), Anadyr/177/2009 (H1N1) and for post-influenza bacterial pneumonia caused by the Gram-positive Staphylococcus aureus. After the infection occurs, its pathogenic features were detected by daily monitoring the mortality (survival) and morbidity rate (body weight loss) and, in addition, viral pathogenesis also was evaluated by assessing virus replication (viral titer) and humoral immune responses (production of pro- and anti-inflammatory cytokines) in respiratory tract of infected mice including during antiviral (oseltamivir) and antibacterial (cefuroxime) therapy. Mortality and virus titer in the infected mice did not differ significantly between the groups of different influenza A virus subtypes. However, production of cytokines (IL-10, IFNg, TNFa) and weight gain proved to be different. Mortality of the mice reached 100% after secondary bacterial infection, whereas IFNg and TNFa levels in mice lung increased reached maximal values in the treated groups. Viral subtype A/California/04/2009MA of influenza A was most pathogenic in mouse model of secondary bacterial pneumonia. Antiviral and antibacterial treatment caused a decrease in mortality, reduced viral titers in lungs, and retain body weight gain of mice. According to these points, the treatment groups did not significantly differ from each other. At the same time, it should be noted that the cytokine production significantly decreased in the treated groups, and IL-10 and IFNg levels in lungs were different, that may be due to therapeutic mechanisms of these drugs. Thus, antiviral therapy for influenza infection and combination therapy for viralbacterial pneumonia can be an effective tool to reduce mortality of influenza.

influenza, Staphylococcus aureus, secondary bacterial pneumonia, oseltamivr, cefuroxime, cytokine

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