I took the first one I had a necropsy done on to the University Poultry center. I had to pay $75 bucks for it. BUT they let me watch and I learned a lot about doing my own. I do them myself now, if I do them at all. I have learned a lot from them about Marak's. With as many people as there are raising birds now, the virus is every where, it blows in on dust and leafs, wild birds carry the virus and so forth.
I simply vaccinate all my chicks upon hatching. It is expensive but it works for me. A bottle of vaccine is around 40 bucks with postage. The vaccine is a turkey herpes virus, closely related but not the same as a live vaccine from Marak's virus.
Think of is like Cow Pox ( the old stories of dairy maids not getting small pox) and small pox. Cow pox is close enough related to fight small pox, same with turkey herpes and the Herpes that causes Maraks.
It is not a perfect vaccine, some may get the disease, I have not had one get it to the point I notice it or they die.
Marak's has been around (identified) since the early 1900's I want to say 1904 or 06...somewhere around then.
It has mutated several times since then, as I recall 4 times since 1970's. At this point the vaccine still works, the mutations have not stopped that yet. Some will tell you vaccinating spreads the disease. I do not buy this. Yes, some birds will live and shed a few cells, but I hardly call that spreading the disease when it travels so far on wild birds, wind etc....
Everyone has to make their own minds up, I have chosen to vaccinate mine.