We have 40 chickens. 3 have the bobble head, going/gone blind, losing weight, etc. symptoms of Marek's. They've probably had it for well over a month and it came on slowly so we didn't realize it. They were supposedly vaccinated, but it doesn't appear that they were. What do we do? Are the rest of the chickens going to develop it? Do we cull these 3? Do we let them live as long as they can? We don't know what we're supposed to do and are very worried about losing the entire flock! Please help!