écologie des virus influenza aviaires en Camargue - IRD

Chapitre IIIreported, in Bewick's swans (Cygnus columbianus bewickii) infected with LP AIV, analteration of foraging and migration efficiencies. For HP AIV, the current knowledge ofpotential virus dispersion through migration is limited to extrapolations from experiments oncaptive­reared ducks performed under laboratory conditions [42]. These birds are thus notsubjected to sustained high energy expenditure and unlikely to experienceimmunosuppression, for which there is increasing evidence in birds undertaking migration[51]. While infected birds might be able to transmit virus over short distances (e.g. duringcold weather periods) [22, 52], more realistic experiments, using birds subjected tophysiological stresses associated with migration, are needed to determine their capacity tospread virus over long distances during seasonal migration.Life outside the hostThe transmission of LP AIV among wild waterbirds is considered to be mainly via the fecaloralroute, with virus particles excreted from infected birds directly into water in feces fromthe digestive system, and contracted by potential hosts by ingestion of the virions in the water[53 ­ 55]. Recent studies have highlighted that HP AIV H5N1 replicates more (and for longerperiods) in the host bird trachea rather than in the digestive tract [41, 42, 44]. Wild swans thathad died following HP AIV H5N1 infection revealed no virus in fecal samples, suggestinglimited cloacal shedding [56], but severe lung congestion and alveolar and bronchiolaredema, together with virus isolation from tracheal swabs, suggested oropharyngeal excretionhad occurred [57]. Preponderance of oropharyngeal excretion is associated with the systemicinfections caused by HP AIV, in contrast to the propensity for cloacal virus excretionassociated with digestive tract infections of LP AIV. Oropharyngeal and fecal excretion thusrepresent two different strategies that may be selected according to ecosystem characteristics.130