écologie des virus influenza aviaires en Camargue - IRD

Émergence du virus H5N1 hautement pathogèneDiscussionTechnological and cultural changes in human populations open new ecological niches forpathogens and inevitably influence their evolution [e.g. 25, 26]. In many host­pathogeninteractions, evolution toward an optimal virulence is likely to occur more or less rapidlyafter successful introduction into a new host species [27]. LP forms of AIV naturallycirculating in wild aquatic birds may indeed become highly pathogenic (at least for H5 andH7 subtypes), after introduction into domestic birds [e.g. 28]. Virulence evolution does notsolely result from this host species switch but is probably driven by a larger set of ecologicalconstraints encountered in artificial ecosystems, such as poultry farming, especially whenintensive, or free grazing duck production (Figure 1). It is thus likely that LP and HP AIV areadapted respectively to natural and artificial ecosystems in which they face differentecological constraints such as host population structure or host species genetic diversity.Natural selectionThe avian influenza virus genome is composed of eight segments of negative singlestranded RNA, coding for 11 proteins [29]. Replication by these viruses is termed "lowfidelity" since RNA mutations lead to a wide diversity of genetic variations in progenyresulting in imprecision in the replication processes [1, 30, 31]. Genetic reassortmentbetween segments of different viruses frequently occurs when host cell is co­infected, and islikely to be an efficient way for rapid evolution and emergence of new AIV in the wild [32,33].The imprecision inherent in AIV replication, combined with the high level of genomereassortment, generates a lot of genetic variants (in terms of gene composition and segment125