Allowing for different lighting, it does appear that it has progressed in that time frame.
Whatever strain(s) I am dealing with have been relatively mild. I have yet to have a paralyzed leg bird. The one in my second pictures does pick her feet up high, and kick them a lot, I am assuming some kind of nerve involvement that makes her feet feel odd. But she gets around fine, finds her food and water (she is in a smaller run so that she can't really get lost) and other than not being able to see, functions pretty normally.
When I first found I had Marek's in my flock my heart sank and I thought that was going to be it, no more chickens. Once I'd had time to really absorb it all, and calm down, I read absolutely everything I could find on the disease, and on the vaccine. Even though some is contradictory, and as I've learned, not every bird presents like the literature, there is a wealth of information. It takes a while to digest it all. The vaccine is somewhat controversial since it doesn't prevent the bird from contracting the disease, it just reduces mortality from it. They can still get it, can still transmit/spread it, can still die of it in some cases. I don't advise for or against it because we all come from different places, have unique ways of doing things and living with our birds, have different belief systems and values. I always say, read as much as you can, educate yourself as much as you can, and make a choice based on what works for you. There isn't one blanket right answer for everyone. I choose to not vaccinate, or bring in vaccinated birds. I usually hatch here, from non symptomatic birds, working to get birds that are more resistant to the disease. That is a long term project obviously. Initially I lost several birds in succession, it was pretty depressing. But it tapered off to only an occasional one. I have one bird left (besides the hen pictured above) that has occular symptoms. So far, no others currently are showing signs. I did bring in some Egyptian Fayoumi's 2 years ago as chicks (unvaccinated), as they are supposedly more resistant to the disease, in the hope they could pass that into my flock (And I'm gonna say, they are definitely not for everyone!). I hatched for the first time this year, making sure all birds were asymptomatic, I don't think I got any mixes, the fayoumi's all stuck together! I did get two more boys, so hopefully they will gather a mixed harem. We will see. I've lost a couple to predators, but so far none of them has shown any symptoms.
But I completely understand why many choose vaccinated birds. Some strains are certainly more virulent than what I've dealt with, with higher losses, and I understand the heartbreak of losing them to something that you can't do anything about once they have it. I've probably lost about a dozen birds, maybe a few more. I do my own necropsies and sometimes there just isn't space in my day to get one done. I always do if there are questions about what it was. I still lose hens to reproductive problems that have nothing to do with Marek's as well. I made a thread awhile back with some images from a necropsy of a bird that I lost to Marek's. She was seemingly fine, went quickly downhill within a week, and was full of lesions. If you want to look that thread is here:
https://www.backyardchickens.com/threads/necropsy-photos-graphic-mareks-disease-for-info.1525851/
Different birds in the same flock can have different symptoms and different presentation. Immune systems are different, genetics are different. It's impossible to predict how long they can survive. With occular symptoms, many of mine have lived for quite a while. With the visceral form, not so long and often I don't know until the end, they hide it so well.
Being a virus, Marek's does what all virus's do and it mutates. There are numerous strains, and it's impossible to know if you have one, or more, and which ones. I don't even think the labs determine which strain, they just confirm Marek's. That is one question that has been raised about the vaccine. Since the birds don't die as often, but still can pass it to others, is it allowing mutations that make it worse? I don't know the answer to that.
Marek's is far more common than most people realize, but it isn't an end to chicken keeping unless that is your choice. There are many of us that have Marek's positive flocks and still have success. It just changes some of how you do things, and maybe some of the decision making. I don't let sick birds suffer. I will try to treat some things, and if it's not getting a response, I won't let them linger with it.
This is a good article written by a member here, my experience has been very similar to hers.
https://www.backyardchickens.com/ar...-i-learned-to-deal-with-mareks-disease.76944/
