The quote in the post above makes a BIG assumption: that the birds that died had prior compromised immune systems. No evidence of that.
I don't call that a big assumption at all. All birds were in the same environment. Only 2 got sick and died (unless I missed something as I skimmed through the lengthy thread.) In any flock situation, there ARE going to be animals that are LESS thrifty, MORE prone to illness. Those animals, simply by definition have a compromised immune system. Not to the point that we consider it to be a clinical diagnosis, (such as HIV/Aids). Consider this: Marek's virus is most likely in all yards. If a chicken gets Marek's at all, it's usually an isolated bird, not the entire flock. Coccidiosis is in all soils. Yet, it's a rare occurrence that an entire flock will get sick. However, if you expose your flock to stressors: moving, crowding, poor feed, poorly ventilated coop, that's when you will see illness. And it will show up in your weaker flock members. Those weaker members have a WEAKER IMMUNE SYSTEM.