One by one my chickens are dying. Two a day, some have symptoms, some don't. I know it's mareks. What do I do? I'm removing lethargic birds, lame birds... It just won't stop. Where does this come from? I bought chicks from tractor supply back in march and last week one of them "hurt it's leg". Then the other leg went...then boom. One after the other they are dropping dead. Please someone tell me everything I'm not looking up about mareks.