Hi, I'm relatively new to chickens. I have a flock of 22 chickens about seven months old. We think they might have been exposed to disease. We also have two different batches of about 25 chicks each waiting to be added to the first in a few weeks to a few months. My question is what do I need to do about adding the younger ones to the flock? I've read some things online about birds carrying diseases. Does that mean I can't ever add them?