Culled a bird this morning -wheezing - what was wrong?

[possumhunter]

I woke up this morning to the strangest sound. I walked outside to find one of my 10 month barred rocks "wheezing". It sounded like it was gasping for each breath. It was just laying on the ground. I heard it sneeze a couple of times. I picked it up and it got a little more lively, but was still wheezing horribly loud. When I set it down it walked around a little bit, but again, still the super loud wheezing. It looked so terrible, I had my husband put it out of its misery. But my question now is, is there a kind of respitory disease that affects chickens? I tried feeling around its throat and didn't find anything stuck in its throat. What could have caused this? I'm worried about the rest of my flock. Thanks!