At the one extreme, those officials have the power to take away a whistleblower's livelihood and destroy their professional reputation. Or they can, in more subtle ways, make their daily work lives miserable by isolating them or denying them work assignments and opportunities for advancement. It seems to have come into use sometime in the late 1960s or early 1970s. Informers, of course, are generally feared and disdained. But they are different from whistleblowers.
Informers act at the behest of officials, and in their own self-interest.
Whistleblowers generally are viewed as anti-authoritarians who act in the public interest, often against their own self interest. Our popular culture reflects the high esteem in which we hold whistleblowers. The films and popular literature glorify the individual who takes on the system at great personal risk. In our culture such individuals are viewed as heroes. As I now describe, our laws and legal institutions similarly reflect the value we give to whistleblowers.