On a new bush you have no idea what stresses it may have been through before it got to your garden so it may be visible then. Yes, if an older bush is growing weaker it could manifest itself. But I have to tell you that I have a 65 year old Pinocchio rose that only rarely shows any signs of it and only in extreme conditions. Yes, there are different symptoms that present themselves. It is rare for a very vigorous, healthy rose to show the signs but I guess it could happen. I have always read and been told that it does not spread from rose to rose in the garden or by contact with tools. There are a few who say otherwise but so far I've seen no definitive proof of that.
The best thing you can do about it is to stop worrying about it. Keep your roses healthy and they will live long, beautiful lives. If you buy grafted roses I can almost assure you that they are infected. Even some own root roses will be if the cuttings were taken from an infected mother plant. If it worries you that much the only other thing you can do is make sure that all the roses you buy are certified as "virus free". And those tend to be a lot more expensive. In your zone it really should not be a big problem. If you're seeing a lot of it please post some pictures of the leaves with the symptoms you are seeing so we can evaluate them.
