écologie des virus influenza aviaires en Camargue - IRD

Chapitre IIIAbstractBackground: Since its detection in 1996, the highly pathogenic (HP) H5N1 avian influenzavirus (AIV) has led to a proliferation of studies, mostly focused on pathogenicity, the geneticbasis of virulence and the evolution of the subtype's genome. Our understanding ofecological factors which favor the emergence and maintenance of such HP viruses is howeverstill limited. Recent surveillance of wild populations in fact reported a virtual absence of HPH5N1, or insignificant levels of circulation, even in south­eastern Asia where the virus isnow endemic in domestic birds.Discussion: While low pathogenic (LP) AIV persist and evolve in wild populations, HP AIVevolve in domestic birds, where they can cause economically serious epizootics that onlyoccasionally spill back into wild populations, generally causing high mortality in infectedbirds. Here, we argue that evolutionary ecology considerations can explain this apparentparadox. Host structure (e.g. density, inter­ and intra­species genetic diversity) andtransmission possibilities differ considerably between wild and domestic birds and are likelyto be the main determinants of virulence selection. Because viral fitness is highly dependentof host survival and dispersion in nature, it is unlikely that virulent forms will persist in wildpopulations if they kill hosts quickly and/or affect host predation risk or migratoryperformance. Finally, virus shedding (excretion via oropharyngeal versus fecal routes) andviral persistence in water suggest differential transmission strategies between low and highlypathogenic AIV.Summary: Human activities artificially shape AIV evolutionary ecology and select for traits(high virulence, host specialisation, etc.) that confer optimal fitness under artificialconditions. Prediction and control of AIV emergence urgently need to consider host ecology122