Unfortunately I, too, have a hen that could possibly have Marek's. I have not read through this entire thread (yet) but will when there is more time. I did read through the related thread about the polish hen that passed last year. I keep hoping to come across a story about a bird being saved, but I have yet to hear that one.
My pullet is 22 weeks. She was a sticky chick and has always been behind the others developmentally. She has always been smaller, and at 7 weeks she was not feathered out well. I worried about her going into winter with no feathers, but finally by 12 weeks she was all feathered out. I believe she is a RIR crossed with a Wheaten Marans. She currently weighs 3.2 pounds, where her hatch-mates are in the 4 - 6 pound range.
About 3 weeks ago I noticed the pullet sleeping in a corner feeder rather than in the hen house. She would also lay in the yard and wait for scratch grains rather than going to free range with her friends. Our young cockerel ( who is over 6 pounds already) is a typical teenage boy and jumps on everything he can get close to. I noticed him jumping on her and afterwards she was limping on her right leg. We assumed she was injured during his romantic attempt. The problem is that he would not leave her alone so we had to bring her in the house. At that point, she was walking pretty well, but it was clear that the left leg was getting "tired" of doing more than its share of the work. She would sit on her hocks and only walk around to eat.
Two weeks ago one of our older pullets (40 weeks or so) started circling. We treated her for a vitamin deficiency, but she deteriorated rapidly. One morning we found her on her back and she couldn't get up. She had been struggling to right herself for some time. We culled her immediately. After we had disposed of the hen, someone mentioned that we should start thinking about some other cause for the illness. There are so many diseases/ailment out there, and unfortunately I didn't think of sending her in for necropsy at the time.
Back to my limping hen, she is not paralyzed, but no longer wants to walk much. When I take her outside she stands in one place and eats grass and after 30 minutes or so we bring her in the house (it is cold out). She curls her toes sometimes, but sometimes she stands normally. When I pick her up I can hear her joints popping (hip joints I think). The weirdest part is that it started out being her right leg that bothered her, but now it is her left leg that she favors and she stands supporting her weight on the right leg. I think they both bother her, which is why she doesn't want to walk.
After writing that whole novel, I am happy to say that she has a voracious appetite, has not lost any weight, and does not show any other signs of illness or respiratory problems. I'm also treating her for vitamin deficiency (just in case) with Vitamin B complex and Vitamin D. A few days ago I was certain she had MD, but now I'm not so sure. How long does it take a chicken from the time they start to exhibit symptoms until they are paralyzed? I'm also treating her with St John's Wort/hypericum although I'm not sure it will actually do any good. I also dewormed the flock this week, and the pullet did have round worms.
While all this was going on, I have two batches of chicks that have been exposed to this pullet and her dander. The whole time I'm thinking, " All my chicks are going to get MD and have to be culled." After reading the info, I was put as ease since my babies hatched here and are from my own hens. IF it is MD, they may have some resistance. They are 2 weeks old and 7 weeks. They are all very healthy. The two week olds are living outside with their broody mom.
I tried to get a video of her "walking" but she is pretty content just laying on her nest in the house. I will try again later.
Thank you to everyone who has posted here. While I would be devastated to lose my little pullet, I know if it is MD it isn't the end of the world. We live on 4 acres so there is no way I would be able to "disinfect" everything. The birds free range, it is in my house, etc. I'm going to be hopeful and treat symptoms as they appear. Hopefully my chicks continue to do well. The bigger they are the harder it is to cull them. Makes me so sad to think about.