2Dogs - we've done the Marek's thing. It sucks. The first chicks we bought from a breeder appeared healthy and were until they hit about 5-6 mos. One lingered forever. I did tons of research about Marek's and found that it is present in the wild bird population...as someone already posted, there are different strains. We lost almost all of that first flock to a neighbor's dog save for 3 - one from the original chicks, 2 hatchery birds we bought as 5 mo pullets (they were not vaccinated). The original chick died suddenly when she was 2 years old and the other 2 pullets are still with us (5+ years old now). We've seen Marek's in the very young birds and the adolescents, as well.
Since those first birds years ago, we've had a variety of chickens come and go (sold - not dead). While we had one hatch (bought fertile eggs under a broody hen) with issues in 40% of the birds, the vet wouldn't say Marek's but I feel like that's what it was - the symptoms were textbook. None of the other birds ever exhibited the textbook Marek's symptoms.
As your girl came with issues, it could have been any number of things. Have you've sent her off to the state to confirm the diagnosis? Regardless of how it comes back, I wouldn't spend energy panicking. Spend that energy making sure your girls are dewormed, have some yogurt/probiotics on board, and aren't stressed in any way. Good luck to you!! And I'm sorry to hear about the little hen.
Finzean - thank you for the information on your experiences with Marek's.
I feed plain yogurt - about 1T per bird - every day.
Since the source of their only possible irritation (new hen) is now gone, my flock should not have any stress aside from wondering why I do not just give them the entire bowl of BOSS instead of just a handful.
I will add the probiotics leftover from Penny to their water & hope for the best.
I will not send the body for necropsy - as you said really no point as there is no cure/treatment.
*friend of bar.ka*RIP all my lovely boys, gone too soon: Steppin' Out 1988-2004 Hey Vern! 1982-2009 Cash's Bay Threat 1994-2009