écologie des virus influenza aviaires en Camargue - IRD

Chapitre IIincludes water­borne and density­dependent transmission on the disease dynamics, with theparameters fitted to the combined waterborne and density dependent model. We removed,step by step, (i) density­dependent transmission and (ii) water­borne transmission, andlooked at the consequences on the dynamics of infections (Figure 3). Removal of densitydependenttransmission leads to high prevalence and the correct dynamic behavior isconserved. In contrast, removal of water­borne transmission leads to an increase ofprevalence from October to May, but at a lower level than predicted with a water­bornetransmission model.DiscussionDensity­dependent transmission is classically assumed for directly­transmitted diseasesdespite some studies showing that frequency­dependent transmission can also explain diseasedata. In this paper, we investigated if these two transmission functions could be involved inAIV. Because these viruses infect mainly waterbirds, and viral particles can persist in waterfor a long period, we also considered water­borne transmission in order to determine the roleof aquatic ecosystems in AIV epidemiology in wild birds.This study highlights that the transmission processes which drive the AIV dynamicsof infection in our study site (Camargue, South of France), involved both a density­dependentand a water­borne transmission component (Figure 1, Table 2). Persistence in water has beensuggested as a possible way of maintaining AIV in wild birds (Wallensten 2007). We indeedsee the importance of aquatic ecosystems in the persistence and transmission of AIV andfurther, our research provides evidence that water­borne transmission drives the dynamics ofinfection in bird communities (Figure 2 and 3).70