finnleyjo Thank you very much.
When a "Live" virus/disease is given, they can shed to other birds. For example ILT in the form they give to Commercial birds, it is contagious, or atleast that is what a past necropsy report gave. Also some of the Mycoplasma's will be contagious and also some of the Herpes virus in birds will pass from one bird to another.
I do not pick my info out of the air, folks may feel this way, but I do not make this crap up.
Find out your needs from the State Vet, your Vet or look it up online. Also asking folks at your area Poultry club as they will know more too.
Good luck.