I have mareks in my flock. I have lost 6 silkies to it always at point of lay and another one is showing signs. My oldest bantam silkie I've had 2 years has somehow survived the disease. I also have buff orphingtons who have been exposed however I haven't lost a single buff to the disease and I've had them 3 years. I've read that orphingtons are also susceptible to the disease however in my flock they haven't. I've also just hatched orphington chicks in my house and hoping they will be the same as my other oriphingtons.
Your Orpingtons must come from resistant stock as they too are also highly susceptible. I sincerely hope that your chick hatching goes well and second generation is also resistant. Time will tell.
Marek's is a horrible, horrible disease. I recently lost a young rooster to suspicious circumstances that makes wonder if MD is rearing it's ugly head again just to remind me that it is still around.