Southern and PC I am so sorry for you two. This just seems to never give you a break. I have been doing a lot of reading and I contacted a friend who is a poultry manager for a national poultry company. When I expressed my concerns he guaranteed me that my flock as well as everybody else's has been exposed. The disease is that prevalent. He talked with me how to clean a flock and it does mean culling but not all at once. And the new flock is pulled from the old, by the means of heat treating the eggs. This takes more time than just culling them all and starting over but is more cost effective.
Here is the kicker, almost all avian wildlife is exposed and unless you run a closed operation with no free ranging the problem will return. It is his contention as the industry that the disease has to be managed as it has gone passed the point of ever being eliminated. I do believe our colder than normal winter for many folks brought the disease to bloom.
I free range my birds and some are in tractors. So far so good, but I bet that all of us with birds especially free ranging are exposed. As much as I hate to say it. And after the harsh winter the posts on illness are bringing this to light. To be honest I have been having my doubts as to getting into chickens for food and pets was a good decision. Some of these birds are just like my dogs, part of the family.
I wish you both the best, and try not to dwell, but make plans if you start over. I don't believe I could.