yes, including environmental diseases. because the environment there is a lot of gamblers, so many other people will also be affected and eventually get addicted too. if you want to really eliminate the addiction, then the environment must also be eliminated from gambling addiction.
One thing you need to be clear that gambling is not a disease only the addiction can be considered as disease since our mind lose the mental control over something and keep asking that thing again and again even it knows that it is not right thing to do and as @jacee it is not like a viral disease which is going to spread also to you when you are hangout with them.If you don't want to be addicted make yourself away.