ANOTHER UPDATE: As of today the chicken is still alive and is showing signs of improvement. The swelling is mostly (or completely) gone. She does not seem to be sneezing anymore either. She is definitely still drinking and I believe she is eating too. I plan to observe her more closely tomorrow to see if she is just pecking at her food or actually successfully eating. Droppings are less watery, perhaps less green colored as well.
I plan to speak with my vet again tomorrow regarding the testing that diagnosed Mareks. I have done my reading on the disease and now I am wondering if the lab gave any indication as to what Mareks serotype was discovered. I am also going to try to contact the hatchery that the chicks came from to see if they will share what (or if) vaccine they used on the chicks. With this info I am trying to determine of there is any chance for a false positive result caused by the vaccine.
Frankly, I think the symptoms of MG, MS, Coryza and AI all fit better than Mareks. But then again all the info I have read makes it clear that symptoms are variable and that all or none of the typical symptoms may be present in Mareks cases.
The reading I've done makes it seem possible that the disease could have come from 1. the hatchery, 2. the feed store (which I can say with certainty was not "clean" enough to believe that birds are not exposed to any number of possible things), 3. my property (which had another flock of free ranging adult chickens on it ~2 months prior to my flock). All things considered it seems my options are:
1. Give up on chickens altogether
2. Cull, intensely disinfect (chemicals, burn coop, till land), wait a long time (perhaps years) and try again with no guarantee of success. Reinfection could occur from any number of sources.
3. Work with what I have, slowly build a flock that is more robust and maybe even breed them for resistance. Obviously this will not be without it's fair share of trouble, heartbreak and frustration.
#1 is my last resort. I really don't want to give up, yet. #2 is an option but the cost, time spent waiting and labor involved with such an uncertain outcome seems too risky. I am leaning towards #3. I only want a small backyard flock for my own purposes: to keep as pets, for eggs, etc. I never planned to sell birds, and with this diagnosis in mind I would obviously completely refrain from doing so.
Am I crazy to attempt to do this?