I believe it is technically "just a cold" in how it affects the sick bird. But it can be passed through a hen to her eggs, and once a bird has it, it will always be a carrier.
Also, if a bird has MG or any "cold" it is likely to be weakened and come down with something else.
Also, if a bird has MG or any "cold" it is likely to be weakened and come down with something else.