Bless you with your chicken problems. I finally yrs. ago gave up on one flock and started over three months later after sanitizing everything I owned three times. Now it is 4 yrs later and I have not had the same problems ever again. It is heart breaking. It is said that Tylan will help in the injectable form but your flock will always be carriers. Every time they are stressed they will again show symptoms and all new birds will get it. Eggs although safe if well cooked to eat will be carriers if it mg/ms. Some of the diseases of resp. can be caught by humans as well be very careful until you know what for sure you are dealing with. I have not been on this forum to know if you have a diagnosis. We just had a guy from NPIP to come to our club meeting and give a class on disease. It was eye opening. Good luck with your flock