écologie des virus influenza aviaires en Camargue - IRD

Émergence du virus H5N1 hautement pathogèneand ecosystem characteristics (natural or linked with human activities) in which these virusesevolve.BackgroundWild birds, and especially waterbirds in the Anseriformes (ducks, geese and swans) andCharadriiformes (gulls, terns, waders) orders, are natural hosts for influenza A (or avianinfluenza) viruses [1, 2]. Avian influenza viruses (AIV) are classified on the basis of genetic,antigenic and structural characteristics of the hemagglutinin and the neuraminidase proteins,respectively involved in the binding of the virus to host cells and the release of new virionsfrom them. Currently, 16 HA (H1­H16) and 9 NA (N1­N9) have been described. For AIV ofsubtypes H5 and H7, two forms of virulence exist: low pathogenic (LP) AIV, generallyconsidered to produce benign respiratory and/or intestinal tract infections, and highlypathogenic (HP) AIV generally responsible of multi­organ systemic infections.Low pathogenic AIV naturally infect wild aquatic birds according to host species,age, immune status, feeding behaviour, pre­migration aggregation and aquatic survival of thevirus [3, 4, 5]. Long term studies performed in Europe and Northern America also revealedsignificant seasonal variation in LP AIV infection rates and circulating subtypes [6, 7].The switch from a LP to a HP AIV phenotype is mainly achieved by the introductionof basic amino acid residues into the HA cleavage site, which facilitates systemic virusreplication. This switch normally occurs within poultry after the introduction of LP AIV H5and H7 viruses, presumably from wild birds or contact with their derivatives [8, 9], and wasdemonstrated experimentally by Ito et al. [10].Since 1955 (and presumably before the virus was characterised), domestic birds have123