Yeah, I know. I've seen that said everywhere. Never made much sense to me, as most smokers don't touch the tobacco leaves, but only get smoke residue on their hands, which seems rather unlikely to carry a virus with it. Furthermore, while I know it isn't possible for every plant to get every virus, it seems unlikely that tobacco-water would be so widely recommended as a remedy for, e.g., aphids, if it were possible for the mosaic virus to survive the tobacco curing and aging process.

So it always just seemed wrong to me. Since then I've heard a couple of (reputable) people say it's a myth, but, unfortunately, without explanation.

So I certainly can't say for sure, but it certainly seems unlikely, and I've never heard an account of how the virus could survive the drying, curing, and burning process which precedes the presence of tobacco residue on the hands of a smoker.