Marek's Found in Flock: Advice Needed

Hi all,

I bought 4 six-week old RIR pullets from a respected online breeder at the end of August. I kept them in their own separate area from my adult birds to let them get up to size before integrating and for quarantine purposes. A few days ago, one of them turned up lame, or so I thought. Maybe it sprained it's leg, I figured. It was eating and drinking normally and still able to walk, although haltingly. After it didn't seem to improve, I started to research lameness in chickens and turned up Marek's. I separated it from the other three pullets and watched it for another day in case I was wrong. It just worsened, becoming unable to stand. To end its suffering, I euthanized it and sent it overnight FedEx to a lab for a necropsy. The results are just in: probable Marek's based on the necropsy. Histopathology will take another couple of days to confirm definitively.

Now I don't know what to do. In addition to the remaining 3 pullets who have been raised with the Marek's bird, I have 8 adult hens, ranging in age from 2-7 years old of which 6 are vaccinated and 2 unvacc'ed (I hatched the 2 unvacc'ed here under a broody).

I've been reading a lot about Marek's, and some sources seem to indicate that if a hen lives long enough, it has probably been exposed to Marek's from somewhere, regardless of how well they are kept, and are probably largely resistant. The main concern seems to be introducing young birds to older flocks, not the other way around as in my situation.

What should I do with the pullets? They seem healthy now, but I look at them as ticking time bombs. Is that extreme? How about my grown girls? I don't want to put the potential carriers in with them, but I can't maintain two flocks--it would be silly anyway because I can't maintain biosecurity on one property.

I know this is long. Thanks for any advice you can give. I can't think of anyone who would want to take on birds who have been confirmed to have been exposed to Marek's, even if they don't have any other birds and never intend to get any more in the future. Nor do I know that it would matter. The barn door's already open.

Thank you for listening!