THE INVISIBLE INVADERS

The Story of the Emerging Age of Viruses

By Peter Radetsky

Little, Brown. 415 pp. $22.95

Viruses are so weird and wily that they fairly cry out for similes and metaphors when you write about them. Viruses are like "minute, wayward, and unruly parts of ourselves -- something like adventurous teenagers who have fled the nest but just can't resist coming back home at every opportunity," writes Peter Radetsky in a typical passage from "The Invisible Invaders." "{They come} sometimes to overstay their welcome, sometimes to wreak absolute havoc, sometimes to make us better through their mere presence. And, like loving parents, for better or for worse, we almost always leave them a key to the front door."

But, as Radetsky himself acknowledges, sometimes metaphors simply get in the way. After describing immune cells as "bodyguards" who dispose of "unwelcome visitors" through defenses "coordinated as precisely as any modern task force," he stops -- just short of hanging himself on his own imagery. "It's clear that a comparison to science fiction may not do justice to the disease-fighting skirmishes that go on constantly inside our bodies," he admits. "These are Star Wars with a vengeance."

The ability to use a metaphor when it clarifies, and to refrain from using one when it would merely confuse, is something that distinguishes a good science writer. And Radetsky, a professor of science communication at the University of California at Santa Cruz, is a good science writer. He understands his elusive subject so thoroughly that his explanations usually sound downright conversational.

Over and over he brings to life the serendipitous nature of scientific discovery. He plots each step of deductive reasoning that brings a scientist from the first experiment to the second, the third, the 53rd. He demonstrates how slowly science progresses, and shows us how maddening it is when it stalls.

Often the tides of science depend on simply following up on a hunch. Louis Pasteur, for instance, stumbled upon a way to weaken the chicken cholera bacteria when he returned from a long vacation and found his cholera culture sitting unattended in a flask. Rather than throw away the germs he knew were dead, he injected a few chickens with the stuff -- and discovered that the birds became mildly ill, recovered, and from then on were immune to virulent doses of cholera germs. Pasteur had discovered the process of attenuation, which paved the way for virtually every vaccine we now use.

This is the kind of book in which juicy anecdotes are thrown in every now and again. Late in his career, for instance, Pasteur saved the life of 9-year-old Joseph Meister by giving him history's first rabies vaccine. The child grew up to become the gatekeeper of the Pasteur Institute in Paris. In 1940, when Meister was 65, the Nazis stormed the institute and ordered the gatekeeper to open Pasteur's crypt. Rather than do so, Meister killed himself.

Radetsky devotes many pages to the early work in virology, beginning with Edward Jenner and his smallpox vaccine of 1796. But he spends time as well with the discoveries and personalities making headlines now, including AIDS researcher Robert Gallo, gene therapy pioneer W. French Anderson and Rockefeller University president-designate David Baltimore, who made his mark as co-discoverer of the mechanism by which retroviruses -- among them the AIDS virus -- reproduce.

Viruses are formidable foes. According to the author, they cause more than 80 percent of all acute illnesses known to man, including yellow fever, polio, smallpox, hepatitis, rabies, herpes, some forms of cancer and of course AIDS. And because most of them are so difficult to see, much less to disarm, viruses have changed the very nature of man's relationship to infectious disease.

A generation ago, when antibiotics and vaccines were first discovered and used, scientists thought they were on the brink of eliminating acute (as opposed to chronic) illnesses. Now they know better. In the face of viruses -- especially those that hide out in cells and may erupt years after the initial infection -- scientists have become humble. Because of viruses, Radetsky writes, "our earlier notions of conquering disease now seem naive and faraway."

The only real drawback of this scrupulously researched, exhaustively detailed book is that it might prove a bit daunting for the casual reader. But it is an impressive feat of reporting for anyone interested in what viruses have done to us in the past, what they might do in the future, and how scientists have managed -- every step of the way -- to fight back. The reviewer, a Washington medical writer, is working on a book about strange new viruses.