plant viruses are ubiquitous.
we inhale plant viruses, animal viruses, plant pollen and fungal spores everytime we take a breath.
tobacco is related to potatoes, tomatoes, they are infected by the same viruses
http://www.extension.umn.edu/distrib...re/dg1168.html

tobacco resins penetrate the skin and you get a picking "buzz", the plant viruses are harmless to humans
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1497768/