MEDICINE: The Killers All Around

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All this bad news is undoubtedly having a cumulative impact on the human psyche. The age of antibiotics is giving way to an age of anxiety about disease. It's getting harder to enjoy a meal, make love or even take a walk in the woods without a bit of fear in the back of the mind. No wonder people pay an unreasonable amount of attention when tabloids trumpet headlines about "flesh-eating bacteria." And no wonder Stephen King's The Stand, a TV mini-series based on his novel about a "superflu" that ravages the world's population, earned some of the year's highest ratings.

The odds of contracting a life-threatening infectious disease are still very low -- at least in the developed world. But the threats are real and frightening enough to spur medical researchers to redouble efforts to learn more about how the many kinds of microbes cause disease -- and how they can be kept at bay.

MICROORGANISMS

It is tempting to think of the tiny pathogens that produce such diseases as malaria, dysentery, TB, cholera, staph and strep as malevolent little beasts, out to destroy higher forms of life. In fact, all they're trying to do is survive and reproduce, just as we are. Human suffering and death are merely unfortunate by-products.

Plasmodium, a protozoan responsible for malaria, flourishes in the human body, growing inside red blood cells until the cells burst. And without enough red cells to carry oxygen through the body, humans become anemic and can die from renal failure or convulsions. Bacteria, which are considerably smaller than protozoans, generally do their damage indirectly, producing toxins that stimulate the body to mount an immune response. Ideally the immune cells kill the bacteria. But if the bacteria get out of control, their poisons can either kill cells or generate a huge immune reaction that is itself toxic.

In an illness like tuberculosis, the immune system kills the body's own cells in the localized areas where TB germs have taken hold, including the lungs or the bones. With staph or strep, the sheer volume of disease-fighting immune cells can overload blood vessels, ripping tiny tears in the vessel linings; toxins can also damage the vessels directly. Plasma begins to leak out of the bloodstream; blood pressure drops, organs fail, and the body falls into a state of shock. In cholera, bacterial toxins attack intestinal cells, triggering diarrhea, catastrophic dehydration and death.

Before the coming of penicillin and other antibiotics, bacterial diseases simply ran their courses. Either the immune system fought them off and the patient survived or the battle was lost. But antibiotics changed the contest radically: they selectively killed bacteria without harming the body's cells. For the first time, potentially lethal infections could be stopped before they got a foothold.