I have 3 one year old hens (1 BA and 2 RIR's) and 4 new girls (2Americauna's, 1 BR, and 1 BA) these girls are our pets and we love them dearly- eggs are just a bonus. This summer we decided to get more chicks since we only had 3 chickens and always wanted to have 6 or 8. So I got 2 Americaunas 1 BA and 1 Barred Rock. Everything was fine until 4 weeks a go the Barred Rock was taken by a hawk while they were outside. I made the most stupid decision to try and replace her. I found a chick the same age from a guy that sells chickens at a local farm swap. The chick seemed healthy and after some time I introduced her/him (yes it turned out to be a rooster and a diseased chick) to the other 3 chicks. 2 days later 1 of the Americaunas and the BA started sneezing and having a runny nose. I started all of them on Duramyacin for what I thought was just a respritory problem and everything seemed fine. 5 days into that antibiotic the BR and the BA started with the runny nose again so I got Tylan 50 injectible. I decided to treat all four with the injections and again everything seemed to be OK. This week I was looking at the BA because she sounded weird- and I realized one of her nostrils was totally clogged! When I cleaned it off the smell hit me and I knew after reading on here and other sites they had Coryza. I looked at and picked them all up to smell them- they all have that awful smell. The older girls and the youger chicks have never been housed together. I know they will always be carrriers, my question is will it kill them? If I integrate the older girls with the younger ones I know they will eventually catch it- will it be more harmful to them because they are older? Or should I just put down the 4 younger chickens because it would be cruel to them to let this diease continue?