Over the centuries, Ken Alibek explains (in Biohazard), armies have used primitive methods to spread pestilence:
The Romans dropped poison into wells to contaminate their enemies’ water supplies. The English gave blankets smeared with smallpox to Indians in the eighteenth century during the French and Indian Wars. Confederate troops in the American Civil War left corpses of animals to rot in ponds along the path of Union forces. And during World War II, Japanese planes dropped porcelain bombs containing billions of plague-infected fleas over Manchuria.
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Soviet scientists combined the knowledge gained from postwar biochemistry and genetic research with modern industrial techniques to develop what are called “aerosol” weapons—particles suspended in a mist, like the spray of an insecticide, or a fine dust, like talcum powder.
Temperature and weather conditions will determine the success of an aerosol’s dissemination. Bacteria and viruses are generally vulnerable to sunlight; ultraviolet light kills them quickly. Heavy rain or snow, wind currents, and humidity impede their effectiveness.
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A bioweaponeer will know to strike at dusk, during periods when a blanket of cool air covers a warmer layer over the ground—a weather condition called an inversion, which keeps particles from being blown away by wind currents.
We packed our biological agents in small melon-sized metal balls, called bomblets, set to explode several miles upwind from the target city.
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Primitive aerosols lose their virulence and dissipate quickly. In our labs, we experimented with special additives to keep our agents from decaying when transported over long distances and to keep them alive in adverse weather conditions.
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We tested a variety of animals, including rabbits and guinea pigs, but monkeys, whose respiratory systems are so similar to ours, were the most effective surrogates for humans. An average person takes in ten liters of air every minute. A monkey inhales four. If four particles of an agent in a given volume of air killed at least 50 percent of the monkeys exposed to an aerosol, we could assume that ten particles would have an equally lethal effect on human beings.
Our standard measure of success for a biological weapon was referred to as Q50, representing the amount needed to infect 50 percent of all exposed human beings in one square kilometer of territory. The Soviet Union devoted an enormous amount of time and money to developing concentrated aerosols that could reach the Q50 level with minuscule numbers of bacterial cells or viral particles.
The most effective biological weapons go on killing long after they are used. Some viruses, such as Marburg, are so hazardous that casually inhaling as few as three microscopic viral particles several days after an attack would be enough to kill you. Biowarfare strategists often look beyond the immediate target to focus on the epidemic behavior of disease-causing agents.
Unlike nuclear weapons, which pulverize everything in their target area, biological weapons leave buildings, transportation systems, and other infrastructure intact. They should properly be called mass casualty weapons, not weapons of mass destruction.