That is so terrible! I'm so sorry. I remember reading all your early posts, and you did everything absolutely right with your coop build, etc.This has been my Marek's journey so far:
I started out with 8 Speckled Sussex chicks I hatched.
One pullet (my avatar) died simply because she stopped eating.
The second pullet died more suddenly but with little outward symptoms.
I was not able to get the first to the state lab but the 2nd said she had tumors indicative of Marek's.
All of the SS flock has symptoms. But some of them are not typical, as per what I've read of Marek's. One has these weird growths on her head that remind me of warts, but they are not like anything I could find online, but I can't think of what else it might be. Not a single other bird shows similar symptoms.
Another has some type of growth on her face that I'm thinking at this point is some type of tumor. I took her to the vet and he prescribed amoxicillin but it did nothing. Then it moved to the other side of her face in her eye, and she looks like she has coryza but she breathes normally and there has always been zero nasal discharge. She is next on the list of potential culls but she maintains weight. Not a single other bird shows similar symptoms. She's been on tylosin for 5 days and zero improvement which makes me think of tumors because 2 different antibiotics have failed to touch these.
A cockerel had something going on with his legs, but he was never paralyzed. I treated him for every vitamin deficiency but he never markedly improved. He was the one I culled.
Another pullet is almost blind and she limps. She does not have paralysis, she acts like the one foot hurts. Not sure how she might have hurt it, she never roosted.
All of them have gray in their eyes now. That was the symptom that sealed the deal with this being Marek's. I have a cockerel and pullet who seem to be otherwise healthy but both have smaller pupils surrounded by gray.
I am attempting to treat them with Chinese Skullcap. I tried to join a Facebook group I found on here but I haven't been approved, so I can't really ask questions of the people who have been doing this.
To have gotten an entire batch of chicks infected with Marek's, which then compromised your entire set-up, is just heart-breaking. Again, I'm so sorry.