[koolba]

The wild is where these diseases tend to originate. But the distribution of populations over thousands of square miles ensures some groups will avoid even the most virulent strains.

The risk and impact to domesticated flocks is increased due to the sheer density of modern poultry operations.

[janice1999]

Not just density but also lack of genetic diversity, as seen in other agri sectors like honey production.

[mschuster91]

Or even plants. Most infamous example are bananas, virtually all banana that you can buy in a supermarket will have the exact same DNA.

[hedora]

High density agricultural facilities provide perfect conditions for producing novel diseases. You have a bunch of stressed animals living right on top of each other, and each one ends up testing out large number of minor variations of the disease until they breed one that’s good enough to escape containment.