écologie des virus influenza aviaires en Camargue - IRD

Chapitre IIIdifferent families [2], suggesting that they are indeed able to infect a large diversity of hostspecies. Under farming conditions, the low (sometimes null) host species diversity is likely toselect for species­specific and/or ecosystem­specific pathogens. Recently, some studiesinvestigated species­related variation in susceptibility (from ducks to passerine birds) andclinical signs generated by an infection with HP H5N1 [40 ­ 42]. Among the bird speciesartificially challenged with the virus, some laboratory­maintained Mallard (Anasplatyrhynchos) presented viral excretion for long periods without clinical or pathologicevidence of debilitating disease [41 ­ 44]. Such results highlighted that, for some HP H5N1AIV strains, high host­pathogen specificity is probably already acquired or at least selectedfor. This rapid evolution of host specificity is believed to have contributed to the spread andendemicity of HP H5N1 in Asia, through domestic ducks [43 ­ 45].Similarly, LP AIV must evolve in the face of intra­specific variability betweenindividuals of a host population. In the wild, immune response is variable among birds of thesame species, depending on their genetic backgrounds, age, activities such as breeding,moult and migration, health status and previous infections with pathogens and other parasites[e.g. 46, 47]. Low pathogenic AIV must be adapted to this diversity in wild birds. Undermany modern farming conditions, on the other hand, potential hosts have low geneticdiversity, highly structured age distribution and are regularly protected from pathogensthrough vaccination and antibiotics. Here again, such artificial conditions, with poor interindividualdiversity, are likely to select for specialist pathogens. Current knowledge on theeffects of intra­specific diversity on AIV evolution is limited to extrapolations fromexperimental studies. These experimental conditions however do not reflect intra­speciesdiversity encountered in the wild and avoid detection of potential individual variation in128