The news that the massacre at Ft Hood was conducted by a psychiatrist prompted the New York Times to ask whether those who treat victims of post-traumatic stress disorder can develop it themselves. The answer seems to be yes, in the form of "secondary post-traumatic stress disorder."
I also wonder about collective PTSD. Can an entire community acquire a higher background level of PTSD, like a kind of low-grade radiation? Can a whole country get a kind of "tertiary" PTSD?
See also former Senator Max Cleland's description of how for soldiers memories of war never go away.