Unfortunately..i have mareks in my birds to. I got chicks last year from what I thought was a " good" breeder. They got sick 1st. I have cemani, serama and brahma. I had put so much money, time, effort into my coops and birds. It was devastating. I think I have a lighter strain. Hits most of my birds around 5 mo. Old. I have had some success using coidal silver and st. John's wort, especially if i catch it early. I also give them vitamins, probiotics and a concoction of herbal tintures that have anti- viral properties. I notice at the onset that some of my birds will start to spend more time "at rest". That's my 1st clue. If I see one laying down more than usual, or detect a slight gait abnormality, iI isolate them and start treatment. I've saved several with this method. Time will tell how effective these treatments work long term.We built the sick ones that survive a coop at the far end of our place. I also clean my coops and spray them down with zircon-s every week. I do put a few down that are crippled or don't do well. I'm opting to breed for resistance. I do have a few 3rd generation chicks..so it will be interesting to see how they do.