What's the opinion of Creationists (who believe that new species do not arise) of virulent cancers?
Canine transmissible venereal tumor cells - originally canine cells that are now a contagious virus.
Devil facial tumor disease - contagious cancer that spreads among Tasmanian devils via facial bites.
All of these are immortal cell lines that were originally cells of the species they infect (with the exception of HeLa which now only exist in labs) and live on in a virulent form.
So the whole "have you ever seen a dog change into a cat?" question - No, but we've seen a dog, a human and a Tasmanian devil "turn into" a virus. Does that count?
And yes, most real viruses are not cellular, these cancerous cells certainely act like viruses, despite their classification.