écologie des virus influenza aviaires en Camargue - IRD

Émergence du virus H5N1 hautement pathogènerabbit (Oryctolagus cuniculus) populations [34, 35], there is no indication that this happenswhen HP H5N1 gains access to wild bird populations.Host diversityThe influence of host population structure in selection for virulence is often critical [e.g. 36].Levels of virulence are determined by and proportional to the frequency with which interhost transmission opportunities arise. Low virulence is typically selected for when host­hostcontacts are infrequent, while high virulence can be selected only when the host contact rateis high [37]. In wild bird populations, contact rates between individuals differ markedlybetween seasons (e.g. reproductive period, migration, wintering), species (e.g. colonialbirds), age, etc. For instance, high bird densities are reached by some species in moulting andwintering areas. These yearly aggregations do not, however, lead to the selection andemergence of HP AIV [e.g. 3, 17]. Compared to wild conditions, host densities in farmingconditions are not only high (even extreme under intensive poultry production), butconsistently so, which may be a major determinant for the selection of high virulence.Networks of poultry production are also likely to favor the persistence of virulent strains,with continuous circulation of AIV between connected markets. Such networks probablyfavor the endemicity of HP H5N1 today in south­eastern Asia [24].In the wild, in addition to variable host contact, and thus transmission, rates, AIVencounter high host species diversity, as in multi­species waterfowl aggregations. The mostefficient transmission strategy in this context is to be a generalist pathogen in order to be ableto infect a large spectrum of host species [e.g. 38, 39], thereby maximizing replication anddispersal opportunities. LP AIV have been isolated from at least 105 bird species of 26127