The only my opinion. These avian viral diseases have been around all along and have been infecting chickens and other domesticated poultry at the same time. In the flock management systems in the past where they birds are in mixed age flocks and not confined in large and densely packed groups, the impacts of the diseases where minimal even though death-loss and productivity reductions did occur.
What has changed is the commercial development of much larger flock sizes maintained at much higher densities and each flock represents a single age-cohort with MINIMAL genetic variation as a result of selection for high and uniform production. These commercial flocks are the ones that are far more vulnerable to the diseases of interest and the main driver for the need of biosecurity as we know it today. As before, our smaller backyard flocks can harbor the pathogens of interest, and potentially be a reservoir from which the commercial flocks become infected.
The commercial flock owners may be trying to protect their flocks by eliminating influence of backyard flocks. This done through restrictions imposed by the government. This is even the case when the far more important vector and reservoir for the diseases are the wild birds.
What has changed is the commercial development of much larger flock sizes maintained at much higher densities and each flock represents a single age-cohort with MINIMAL genetic variation as a result of selection for high and uniform production. These commercial flocks are the ones that are far more vulnerable to the diseases of interest and the main driver for the need of biosecurity as we know it today. As before, our smaller backyard flocks can harbor the pathogens of interest, and potentially be a reservoir from which the commercial flocks become infected.
The commercial flock owners may be trying to protect their flocks by eliminating influence of backyard flocks. This done through restrictions imposed by the government. This is even the case when the far more important vector and reservoir for the diseases are the wild birds.