I had a flock of 25 chickens, various breeds some for more than 2 years. Raised on organic feed and loved. I wanted a deep brown egg layer and found a local backyard chicken for sale, French Maran pullet. I should have been more careful and quarantined before add to flock but too late. I thought I heard her sneeze and rattle but seemed to recover but within 2 days a hen or two appeared to have difficulty breathing, one quite bad. I brought the sick one up to the house and nursed it but it died within 24 hrs. I had started Tylon 50 injections twice daily to all the birds and we are on day 4. No more have died but everyone is infected, some worse than others with rattling, swollen body parts, sitting around puffed up. Slow to recover but holding on. Anyone have any additional suggestions? Heartbroken as you can imagine..