to profit margins for most of the poultry industry (see Swayne and Sibartie in Chapter 4; Swayne, 2004).

Preventing Interspecies Transmission

The intersecting and sometimes conflicting interests of commerce and public health were also evident in discussions on preventing transmission of avian influenza from wild to domestic birds, and from poultry to domestic animals and humans (for transmission pathways between species, see Figure S-4). Because wild waterfowl can carry the influenza A virus without developing signs of infection, influenza cannot realistically be considered an

FIGURE S-4 The reservoir of influenza A viruses. The working hypothesis is that wild aquatic birds are the primordial reservoir of all influenza viruses for avian and mammalian species. Transmission of influenza has been demonstrated between pigs and humans and between chickens and humans but not between wild birds and humans (dotted lines). There is extensive evidence for transmission of influenza viruses between wild ducks and other species (solid lines). The five different host groups are based on phylogenetic analysis of the nucleoprotein genes of a large number of different influenza viruses.

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