Fig. 1
From: Wild bird surveillance for highly pathogenic avian influenza H5 in North America
Conceptual model of the process of introduction and wild bird dispersal of HPAI and subsequent infection of commercial poultry holdings. The rectangular boxes (1-3) represent probabilities and the circles represent external factors that influence the probabilities. It is unlikely that direct transfer between waterfowl and poultry occurs. It has been proposed that “bridge species” that interact or share habitats with wild waterfowl and occur on poultry farms facilitate the transfer [14, 15]. Potential bridge species may be birds, rodents, and/or invertebrates