Jonathan Tucker, director of the Chemical and Biological Weapons Nonproliferation Program at the Monterey Institute of International Studies in California, lays out the entwined history of smallpox and humanity in his latest book, Scourge: The Once and Future Threat of Smallpox. He recounts the battle to eliminate every single case of smallpox infection on earth, and the uncertain future of that vicious virus. By the time readers finish this book, they will likely be as worried as Tucker is. Smallpox is the viral sword of Damocles hanging over all our heads.

Some diseases are simple nuisances. Others are slow and insidious. Smallpox is acutely apocalyptic. The virus is highly contagious and highly lethal. Those it fails to kill outright are left disfigured or blind. And the bodies of the dead are as infectious as the dying. Centuries ago, this massive (for a virus), dumbbell-shaped microbe cut a genocidal swath through the New World when the conquistadors landed. Between 1492 and 1800, writes Tucker, the estimated native population of the Americas plunged from 72 million to 600,000. The Native Americans had never been exposed to smallpox or measles or, later, to the yellow fever virus that arrived with African slaves. Primitive firearms and cheap whiskey may have helped Europeans to enter the Americas, but smallpox broke down the door.

The accidental discovery of a primitive form of smallpox vaccination (called variolation) in the late 18th century gave people a glimmer of hope that the disease could someday be controlled. Widespread vaccination began in the 19th century, and compulsory vaccination programs in the 20th century rid the Western world of regular outbreaks and deaths. In 1958, then Soviet deputy minister of health Viktor Zhdanov made the first formal proposal to eradicate smallpox. It was a reasonable plan. There were only a few remaining endemic countries, but smallpox-free countries were still spending time and money to vaccinate their citizens and guard their borders against infected travelers.

D. A. Henderson, a physician in the U.S. Public Health Service, was handed the assignment. "Suppose I refuse?" he asked his boss. His only choices were to resign or move to Geneva, Switzerland, and run the Smallpox Eradication Unit. Fortunately, he chose Geneva.

Scourge is good history because it can be read as the history of one man and the forces he marshaled - and those he overcame - in order to wipe out smallpox. Tucker's portrayal of those battles is intimate and fast-paced. He has listened to Henderson's oral history and to the stories of other key players in their campaigns of viral search-and-destroy. Indeed, many of the gray-haired veterans of the smallpox campaign can still be found in Baltimore, Bethesda, and Atlanta. Henderson is at Johns Hopkins, as director of the Center for Civilian Biodefense Studies.

Henderson's battle was not just against a virus. It was also against the World Health Organization (WHO) bureaucracy, deceitful health officials, superstitious tribesmen, bandits, and primitive Third World infrastructures. Threats, sarcasm, and outright badgering were useful tools in dealing with officials reluctant to admit they had smallpox cases.

By the spring of 1978, the last naturally occurring case, a Somali cook named Ali Maalim, was found and vaccinated. On May 8, 1980, smallpox was officially declared eradicated. (Senior WHO bureaucrats were doubly relieved; Henderson and his brash, freewheeling colleagues would also be gone from their genteel organization.) At the same time, the WHO also called a halt to routine civilian vaccination.

Which brings us to today and the susceptibility of the world's population to smallpox. When vaccination stopped, immunity waned and vulnerability increased. To reduce the chances of an accidental release of the virus, most research on variola viruses stopped and the stored samples of smallpox were either destroyed or turned over to two designated repositories, one in the U.S. and the other in the U.S.S.R.

It turns out, however, that we were in greater danger than we realized. In 1989, a Soviet defector alerted British and U.S. intelligence to a secret Soviet bioweapons program that was staggering in its scope. Biowarfare agents, including smallpox and anthrax, had been prepared on an industrial scale. Secret labs and factories had produced metric tons of smallpox virus for delivery by ballistic missiles. Tucker writes, "A Soviet attack with smallpox weapons against urban targets would have dealt a devastating blow to the United States, perhaps destroying it as a functioning society."

Not many people outside the military and intelligence communities knew about the Soviets' program to "weaponize" smallpox. In 1990, then Health and Human Services Secretary Louis Sullivan innocently proposed sequencing the smallpox genome and then destroying the remaining virus stocks. But like a condemned killer on death row, the virus repeatedly has had its execution stayed as new appeals were filed to defer the day of reckoning. The first execution date was June 30, 1995. In the U.S., quiet but intense arguments were being made to preserve the stocks against a growing fear of bioterrorism. Much of that fear was generated by the confessions of a Soviet defector, Ken Alibek, and by Richard Preston's bioterrorism thriller The Cobra Event. Major policies are made of such minor things. The execution date came and went as research and arguments continued.

Readers of Scourge will get a blow-by-blow, behind-the-scenes account of how obscure government officials, a book-loving President, an opportunistic defector, and D.A. Henderson struggled with one another over the fate of smallpox. It is a gripping look at decision-making by someone who has been through it himself. Tucker is a veteran of the State Department, UNSCOM's post-Gulf War search for Iraqi bioweapons, and a presidential advisory committee on Gulf War syndrome.

There are good reasons for destroying the stocks; there are also good reasons for not doing so. Sometimes facts can carry you only so far. What seems to drive the smallpox debate now is not tangible data, but visceral fear. The new execution date is December 31, 2002. In the meantime, the U.S. smallpox stocks remain locked up at the Centers for Disease Control and Prevention's Building 15 - a building Tucker describes as being able to "withstand an earthquake, a tornado, or an airplane impact."

The smallpox eradication program ended infections and the need for vaccination, but it did not eradicate the virus itself. Perhaps we should drop the word "eradication" in favor of something less absolute. "Containment" perhaps. We will never be able to account for every single smallpox vial on earth. Moreover, the genomic sequences have been published online; in the near future it should be possible to recreate the virus from scratch.

The history of smallpox is a tale of noble deeds and utter villainy. Tucker's book is an important and timely review of that history - made all the more so by the events of September 11. It may be some time before the last chapter of that history is written.