If your birds have Mycoplasma, there is a good chance that the eggs you hatch are immune, yet carry that virus. I have been looking into these subjects for a while now. If you give them the vaccine, you will have carriers.
From what I understand, Maine is all I can speak about, I was told that it was almost a 99% probability that my birds are positive for MS/MG. I will not show mine, nor take them from my property, so strict bio-security to prevent any more disease to run my flock.
The wild birds, chickadees, wild turkeys etc have MS/MG and spread it to our birds. One of the only ways to prevent it is to have them tested, negative and then put them in an enclosed building with strict Bio-Sec.
Basically, the hatcheries that we get our birds from- be it large or small hatcheries, they do not test for MS/MG only pullorum/typhoid (NPIP tested) birds.
These virus' will not "kill" your birds, yet can affect egg laying, CRD etc. Stay away from Commercial "battery" hens for laying, they carry many injected forms of these diseases along with ILT- a nasty condition that will leave you with real problems.
Oh, and if you look at the emergency/illness/cures section on this site, most of us have MS/MG and people have not culled (why bother at this point) and it has been spread to all corners to USA- dunno about Alaska or Hawaii!
There is a link below by my name on 1 of the articles I've been muttering and typing about these diseases. I hope to someday write a paper on it, oh, write to your state Veterinarian about your concerns, as its a health issue that we need to address in the US.
Be well, Good luck and take care!