Although Rowan doesn’t show up in this info page, he’s the only character who’s canonically had the Whispers — as recounted back in Time and Tides.
The longer name is “Spiritually Transmitted Acute Dysphoria,” or STAD.
Leif: Thorn, what’s “The “Whispers”? And should I be scared?
Thorn: Well, it’s a magical disease, and — The key symptom is an acute, usually paralyzing sense of hopelessness. So it’s pretty scary, yeah.
It has a longer scientific name, but it’s mostly called “the Whispers” because you catch it from infected spirits that “whisper” in your ears. Certain non-magical treatments can make it harder to catch — but the only cure is a magical girl with special healing powers.
It isn’t contagious between humans! Only spirits can transmit it. And even then, mostly between other spirits from the same domain. So if you’re in a region of Northern magic, you’re safe — they can’t get in.
But if a human is already infected . . . just relocating to a region of Northern magic won’t cure them. Neither will therapy, or chemical antidepressants. You need a magical girl.
Leif: So I could catch this, any time I leave the Embassy grounds? You could catch it all the time?!
Thorn: Only when there are infected spirits around to catch it from! This is the kind of thing we have health departments for.
Our spirit-based utilities (plumbing with water spirits, heat and lighting with fire spirits, waste disposal with nature spirits) all have filters. And national safety regulations. Any sign of infection can be isolated, then health officials can show up to sanitize it.
As for contagion from wild spirits . . . At least in Ceannis, “catching those early” is one of the Department of Prophecy’s top priorities.