Illnesses usually are obtained in your environment, from exposure to the disease. It might be from another chicken or a visiting wild bird. Some people track in diseases on their shoes from shows or feed stores, or other ways. Sorry that you are dealing with a contagious disease, but your flock should remain closed and no chickens should be shown. You always have to assume that even chickens who do not show symptoms are carriers.
I would really hope that this is obvious to EVERYONE. Unfortunately, a lot of times profit is more important than ethical behavior for some.
I seriously doubt that I tracked "possible" AVL in from a feed store and I don't have any friends that I visit that have chickens. I actually don't really have many friends within a 3 hour drive but I digress. I also have not even started showing yet. That was my goal at some point (just my silkies).
Sure, it could have possibly come from a wild bird, a fly, a mouse... Who even knows. Luckily it does not live very long in the environment and now I am seriously considering culling my entire flock and walking away from chicken keeping all together.
It is strange that only one chicken out of 4 had these symptoms. I'm not saying that my rooster didn't have it, please don't misunderstand, I'm just saying it's bizarre. It also bugs me that the vet never said anything about my whole flock could have AVL or even that I should consider culling. His ONLY statement on the phone, regarding that specific issue, was that it was not typical of AVL but that he also could not completely rule it out.
I only had the other birds done to see if it was a "flock" issue.
It has made me hyper paranoid!
I'm curious as to whether I can have my flock tested WITHOUT having a necropsy done on them.
My silkies are separate from my other flock thankfully!