I know that this is a common question, as everyone always supplies Marek's as a possible cause of illness. I've had three hens die, and another is currently sick, all within the last 2 months. Each one is showing different symptoms from the last and it's really throwing me for a loop. My current thought was E Coli causing different problems in the hens, but now I'm wondering if it is Mareks. The three that died were varying ages. 25 weeks, over a year, and over two years old. The youngest I found huddled up one day and feeling pretty thin when it had been bouncing around crazy the day before. It suddenly seemed as though it couldn't see (Which is the main reason I'm wondering about Marek's). It seemed to be doing fine in isolation and was eating/drinking/gaining weight for nearly four weeks before suddenly dropping dead. The one year old's main symptom was very heavy breathing. She would take large rapid breaths with her mouth open. Stool was runny yellow with a few green chunks. Refused to eat. Sat huddled up with eyes closed. The two year old was fluffed up and off her appetite, breathing fast but not heavy. Her lower abdomen was slightly distended and squishy, poop was yellow and white paste like consistency before getting runnier close to her death. For her I was originally thinking egg yolk peritonitis. Now the current one I had immediately taken from the coop when she didn't come running to greet me like she usually did. Was still walking around and eating, but she was usually always up in my face so it was weird enough for me to bring her inside. Poop was normal looking brown albit being a tad green. Wasn't too runny or hard. She was eating heartily (crumbles and cooked egg mixed with yogurt) up until this morning, and now she is suddenly leaning back on her haunches unable to keep her weight forward (The second thing that makes me think Marek's). Poop is watery. None of the other hens showed any sign of paralysis of any kind. I've treated with Tetracycline first, then when that was done tried Corid just in case. I ordered Baytril and am waiting on that. I also wormed everyone just in case. Do you think maybe this could be Mareks? There haven't been any new chickens introduced in well over a year.. the last couple babies were hatched from my own eggs. No new stress other than it being winter. Coop is kept clean, good airflow and free from drafts. The other's poop has been pretty normal. Maybe a tad pinker or runnier in some, but nothing that would normally make me worry. Just worried and frustrated! Any insight is appreciated.