The question this raises is: Why aren’t more people dying from Sin Nombre virus? The answer seems to be that, although very dangerous when caught, it’s not easy to catch, despite its presence in mouse-infested sheds and trailers and garages and barns across much of America. This is because it doesn’t pass from person to person — only from mouse to mouse, and from mouse excretions to one unlucky person or another, each of whom represents a dead-end host. (The “dead” of that “dead-end” may be figurative or literal.) It’s not a “very rare” virus; it’s a common virus known only rarely to infect humans, and with no ramifying chains of human contagion. So the Next Big One is not likely to be Sin Nombre.

Nor is it likely to be Ebola, which is transmissible from human to human through direct contact with bodily fluids, but can be stopped by preventing such contact. Furthermore, Ebola burns so hotly in its victims, incapacitating and killing so quickly, that it is poorly adapted to achieve global dispersal. Only one human has ever been known to leave Africa with a rampant Ebola virus infection — and that was a Swiss woman, evacuated in 1994 to a hospital in Basel. If you want to be grateful for something today, be grateful for that: Ebola doesn’t fly.

WE should recognize such blessings, and try to focus our deepest concerns on real global dangers. Too often, we’re distracted from good scientific information by yellow journalism and the frisson of melodrama. Ebola is charismatic, the demon that people love to fear. Other lurid candidates, like hantavirus and SARS, also get their share of headlines. When you mention emerging diseases, people’s responses tend to fall at the two ends of a spectrum. Some folks are mesmerized by the dark possibilities and the garish but unrepresentative cases. Others are dismissive, rolling their eyes at the prospect of having to contemplate still another category of dire monition. They want you to cut to the chase. “Are we all gonna die?” they ask. Or they say: “Fine, so what can we do about these bugs?”

Yes, we are all going to die, though most of us not from a strange disease newly emerged from a mouse or a chimp. And there are things we can do: get a flu vaccination; support calls for research; avoid coughing people on airplanes; apply mosquito repellent; wear a mask when you sweep out your old shed; don’t eat any chimpanzee meat from an animal found dead in the forest. But the concrete measures are limited by time, place and circumstance. The broader response is more basic: learn, absorb, understand. Don’t start trying to apply your knowledge until you have some.

Among the other unsettling disease news this summer, you’ve probably seen mention of influenza, that old familiar zoonosis, quite capable of devastation and melodrama all its own. Yes, there’s a new flu bug, a nasty variant of the H1N2 strain, suspected now to be traveling through pigs at state fairs. The influenzas are protean and explosive. Keep your eyes on that one.

Hantavirus in Yosemite is a little cloud that seems likely to stay little. This doesn’t mean that the great dark thunderhead isn’t coming. It just speaks to the need for a bit of informed judgment about which sector of the horizon we should watch.