écologie des virus influenza aviaires en Camargue - IRD

Chapitre IIIbeen victims of recurrent outbreaks due to HP AIV [11], generally limited to localised areasbut responsible for high mortality and substantial economic losses. By contrast, wild birdshave rarely been involved in HP AIV infections. Before 1996, only one HP AIV outbreak wasdocumented in the wild, leading to the death of c. 1 300 common terns (Sterna hirundo) insouth Africa [12]. Since that date, the emergence and the spread of the Asiatic lineage HPH5N1, first discovered in domestic geese in southern China in 1996, has been responsible forthe death of more than ten thousand wild birds, sometimes through mass mortality events(e.g. lake Quinghai, China, in May­June 2005; [13 ­ 15]). Detection of HP H5N1 in freelivingwild birds remains however a rare event. Extensive surveillance of wild populationshas failed to detect this subtype [7, 16 ­ 18], even in areas where the virus is endemic indomestic birds [19, 20]. The few reports of asymptomatic infection by HP H5N1 in healthy,free­living wild birds lack important substantiating information [21] and such cases ofinfection have yet to be convincinly demonstrated.Although some recent studies have focused on environmental factors that contributedto the spread of HP H5N1 from (and within) south­eastern Asia to Europe and Africa [e.g.22 ­ 24], our general knowledge concerning mechanisms of emergence and persistence of HPforms is still limited. Here, we argue that because the ecological landscape in which AIVevolve is totally different between natural (i.e. wild birds) and artificial conditions (e.g.intensive poultry farming or free grazing ducks), specialization processes occur. Thesephenomena, whose directions are predictable from an evolutionary ecology perspective, arelikely to explain both virulence heterogeneity among AIV and why HP forms do notnaturally emerge or persist in natural ecosystems.124