I have two flocks right now, one older flock made up of 6 one year olds and a younger flock of 11 two month olds. They live 60 miles from one another, but I see both twice a week. I'm very involved in the care of both and routinely handle both flocks. While I change my shoes most of the time for both flocks (wearing a pair of shoes at one house for the one flock and another pair of shoes at my other flock's home with another pair of shoes in between), sometimes I might wear my in-between shoes to both flocks. In addition, my older flock once lived where my younger flock now lives (about 9 months ago). I'm noticing possible marek's symptoms in my older flock and have actually lost two or three to what looks like it and my lose another shortly. There are tons of large scale chicken farms around where my flocks live and I've noticed other small flocks in the area as well. I got my older flock from an auction when they were around 2 months old. I got my younger flock of silkies from TSC during chick days. This all leads down to a few questions: Is it possible for my younger flock to already have been exposed to marek's and be building resistance? Is there anything I can do for my older flock now? Can I still vaccinate my 2 month olds? Is there any point in vaccinating them now? Will I be able to put the two flocks together without worrying about marek's spreading? Is it normal for chickens around 1 year old to start developing symptoms of marek's? Could it be another virus or problem I am unaware of? They frequently start having problems standing, walking, and using their wings and then die within a week. At this age, I would have expected to see symptoms a lot sooner. Could it be that they only were exposed to it once they moved to their new location 60 miles away from their original home?