Why is avian influenza spreading so quickly in some regions and not in others? What are some possible ways that it may spread globally?

1. Some regions have poultry facilities that are not very well kept with a high density of birds, and that are unsanitary.

2. Infected birds contaminate people, then the virus can move by clothing, boots, vehicles. We shouldn't forget that those birds (and their meat) can be sold all over the world.