BOOK REVIEW : The Human Adventures in Ages-Old Wars Against Viruses : THE INVISIBLE INVADERS: The Story of the Emerging Age of Viruses, <i> by Peter Radetsky</i> . Little Brown and Co. $22.95, 415 pages

Physicians have fought viruses with vaccination since Edward Jenner inoculated a young milkmaid against smallpox in 1796 (the word vaccination, in fact, comes from the Latin vaccinae , meaning small pox ) .

But no one ever examined a virus visually until the invention of the electron microscope in 1939.

What was observed, according to Peter Radetsky, was “nothing less than a submicroscopic missile, armored with protein, at the heart of which is a clear jelly of nucleic acid, the essential genetic information of life itself.”

Starting with the story of smallpox and continuing through the epic of the discovery of the polio virus, the Epstein-Barr virus and the AIDS virus, Radetsky, a journalist who teaches in the science communication program at the UC Santa Cruz, explains the human adventures in discovering, combatting and suborning viruses in his superb new book, “The Invisible Invaders.”

Most epidemic diseases occur when an alien agent enters our bodies.

When the agent is a bacterium, it can be stopped dead by an antibiotic. But when the agent is a virus--a smaller and more insidious organism--the only defense is offense.

For once inside a cell, viruses capture the cell’s genetic material and proceed to undermine the immune system, or sometimes trigger cancerous growth.

Offense in the matter of viruses means injecting deactivated or dead viruses into an uninfected individual.

This triggers the body’s immune system to produce specific antibodies to keep the virus at bay.

Radetsky describes the death of Louis XV from smallpox in 1774 and follows the king’s body to its unceremonious entombment.

The disease rots the body even as the patient is living, and in death produces such a stench that it was said to have killed one of Louis’ gravediggers.

Radetsky moves on to Louis Pasteur who, in finding a cure for rabies, established the concept of “carriers” of disease, individuals who have the virus but exhibit no symptoms.

The phenomenon was verified in the case of “Typhoid Mary,” a woman who spread the fever without falling ill herself.

Never too hurried to leave a story incomplete, Radetsky describes Joseph Meister, the small Alsatian boy whose life was saved by Pasteur’s gamble, and then adds one of many “Postscripts.”

In 1940, 55 years after his rabies shots, Meister was working as a guard at the Pasteur Institute when the Germans arrived in Paris.

Rather than admit the Nazis, he committed suicide.

Radetsky weaves historical anecdote and capsule descriptions of the virus doctors into each chapter.

The chapters lead smoothly from one to another, occasionally doubling back to remind the reader of what went before. And all along we learn about the way different viruses behave--some, like flu, able to dodge antibodies by undergoing mutation.

Two of the dread viral epidemics of this century, polio and AIDS, have provoked ugly discord among the researchers racing each other to find a vaccine.

Radetsky untangles the stories of Albert Sabin and Jonas Salk, explaining the differences between the two men and the two vaccines, the political issues involved, and the possibility that some combination of the two approaches may soon become standard procedure.

Similarly, he sorts out the chronological narrative in the story of the identification of the AIDS virus by the American Robert Gallo working at the National Institutes of Health and the Frenchman Luc Montagnier at the Pasteur Institute.

Radetsky is scrupulously nonjudgmental, describing the human side of these scientific enterprises without losing sight of the goals of all the participants--the achievement of a safe vaccine.

Radetsky draws a vivid picture of the British missionary physician Denis Burkitt, who covered thousands of miles along central African roads in 1960 to track down the territory of a killer of African children, a disease now called Burkitt’s lymphoma.

Burkitt’s work drew the attention of another Englishman, M. Anthony Epstein who, in collaboration with Yvonne Barr, discovered the Epstein-Barr virus in Burkitt’s victims and later elsewhere.

The Epstein-Barr virus turned out to be the first virus known to be widespread and often harmless, except in special cases.

In the course of reading about hepatitis vaccines, Epstein-Barr and the genetic engineering of viruses, the reader will recall, with the aid of excellent illustrations, the functions of DNA and RNA, retroviruses and cancer-causing oncogenes.

It is impossible at this point not to ponder the evolutionary implications of viruses.

As ancient as our own DNA, they may well act, Radetsky suggests, as “agents of evolution.”

Next: Jonathan Kirsch reviews “The Hidden War” by Artyom Borovik (Atlantic Monthly Press).