écologie des virus influenza aviaires en Camargue - IRD

Chapitre IIDifferent studies within the Mediterranean wild bird populations revealed low prevalences (1to 4%) of AIV infection (De Marco et al. 2004, Lebarbenchon et al. 2007a) but a recentpaper highlighted a higher prevalence (up to 12%) in Northern Europe (Wallensten et al.2007). Hence, the prevalence observed in our study area cannot be due only to a migratoryprocess. The introduction of infectious individuals within our study area should not exceedone percent at most and if we consider one percent of births as Infectious we obtain similarresults for our analysis.The duration of AIV immunity in wild birds is not well known, but we can reasonablyassume that immunity will be mainly subtype­specific and that given the high mutation rateof AIV (Chen and Holmes 2006) immunity escape might occur every year. Thus, immuneprevalence should not be higher than maximal infectious prevalence observed elsewhereduring one season. This leads to include a factor of vaccination rate at “birth”. The analysisof a community with an introduction of thirty percent of immune individuals (suggested byDe Marco et al. 2004) at birth does not change results.Assuming that a population increase leads to no deaths is a very strong hypothesis.However, we tried to add constant birth and death rates to this forced demographic parameter(i.e. b m =b m +c and d m =d m +c). We included into our different scenarios the maximal birdlifespan recorded in the Camargue (c = 20 years­1). Table S1 presents the values of b m andd m .Parameter estimationsFor simulations, we started our model at the disease­free equilibrium (S = N, I = R = B = 0)with one infectious bird. Assuming that transient dynamics go on during ten years we ran our84