[yankoff]

Perhaps, a better way to traverse this would be to look at the history of virology, trace main events, starting from the discovery of bacteriophage, and check out associated work. It is hard to say what kind of evidence would satisfy you. Viruses have been isolated many times, and transmissibility has been shown on cell cultures and animal models.

You can't purposely infect real people with disease-causing viruses in research so you won't find much studies like that. But there is no doubt that viruses are transmissible and can cause disease, and there is plenty of evidence to support that. Check out studies on yellow fever virus and flu done more than a hundred years ago.