We've never had one like this .
We've looked through B.Y.C. posts and only seen a hypothetical guess of another's query stating Mareks .
However , according to a vetmd reference site the vet stated that Mareks had to have more than just liver damage .
They stated that Mareks would be identified...
Opening info;
1) 2 Yr. Old English Jubilee Rooster / GreenFire Farms bloodline .
2) Developed this fixture while in isolation through our shut down period.
3) We have over 300 birds , over 40yrs. In the fowl world , never experienced this one.
4) No one else has this , not his girls in his flock...