Yep! And perhaps the wizards were attempting to create new talents which then would have been able to be passed down through generations, but what they got was the contagious spreading of these altered talents that would only serve to make people with "new" talents ill?
For spreading purposes, maybe it could spread when one uses their talents on another, this contaminating the other person's talents with the reverse ones? Oo! That could work the other way too, like if a healer tried to heal a reversed talent person with Healing, his/her talents would just get contaminated and not do any good at all! :)