In the second book of Dean Koontz's unfinished moonlight bay trilogy, there is a retro virus that takes DNA from one creature alter itself accordingly and deposits itself into another cell, causing it to pump out more of itself and altering the cell's DNA.

The result is that humans become animalistic, and animals start to gain above average intelligence. Not by a great amount, but by enough to be noticed.

Is this possible? Or is this actually science fiction?