I have a flock of 45 chickens and 10 guineas. I was looking at buying 5 more chickens that are 4 months old. they are vaccinated against mareks and cocci. I am not sure if my current birds are vaccinated. They came mostly from local feed stores and online. I know the ones online were vaccinated for cocci. There are 3 that I hatched also that are not vaccinated for anything. My question is..if I bring vaccinated birds into the flock can it spread disease through feces to the other birds? there are also 4 ducks on the property that free range that came from the feed store. Thank you in advance!