CO-EVOLUTION. “There are many animal polyomaviruses, and polyomavirus infection is highly species specific. This suggests prolonged coevolution of humans with at least five different polyomaviruses. Similarly, the eight known human herpesviruses are extremely efficient at establishing chronic infections; most of us carry many herpesviruses for our entire lives.”
http://www.sciencedirect.com/science/article/pii/S0092867409007831