MS/MG is treatable, and while they still technically are carriers, I have never found a relapse in a flock after treatment or just recovery. There is a vaccine and maybe infection is sort of a vaccination as well.When I got my chicks from them two years ago, the only chick died was my Houdan. I was so sad, since she was the one my son really wanted. And all my chicks had some respiratory disease (maybe MG?). I think it might from my Dorking, since they got rid of their Dorkings a couple months later. Now my entire flock has it. Luckily, it's a very mild strain and only cause some sneezing and runny nose.
I looked into the vaccine, but it is very expensive and will result in a positive test the rest of the bird's life. Since vaccinated birds are so rare, it would be hard to explain that the positive test results are actually good.