Not only water supplies are susceptible to premeditated contamination; so too is much of the air we breathe. Skyscrapers, tunnels, subways, and their requisite heating and air-conditioning systems provide targets and also avenues of attack for would-be bioterrorists. This potential was demonstrated by the United States Army during the 1950s, when it released the harmless bacterium Bacillus subtilis into some of the subways in New York City and subterranean passageways in Washington, D.C., and then monitored the spread of the bacteria. The experiments demonstrated that such public spaces are vulnerable to attack with biological agents.
The air-conditioning systems of large building complexes may be just as vulnerable to attack as subways and tunnels. Again, no evidence exists that bioterrorism of this sort has occurred, but the example of legionnaires' disease is instructive. When 221 people, most of them guests at a single hotel in Philadelphia, developed an unusual pneumonia following an American Legion convention in July of 1976, a crash program of research revealed that all of them had been infected by a previously unknown bacterium now called Legionella pneumophila. Intensive investigation eventually showed that the bacteria had contaminated the water source for the air-conditioning system of the hotel, and the air-conditioners had spread the bacteria to the guests. Most outbreaks of legionnaires' disease since then have also been traced to water and cooling systems in hotels, hospitals, and businesses. Clearly, unprotected systems of this sort offer a potential target for the bioterrorist.
People need not be the primary targets of bioterrorism. On December 6, 1989, a panel of scientists led by Roy Cunningham, of the U.S. Department of Agriculture, and including Caroll Calkins, of the department's Insect Behavior Unit, in Gainsville, Florida, met in Los Angeles to discuss possible reasons for a very peculiar pattern emerging in the spread of the Mediterranean fruit fly. The Medfly, as it is commonly known, constitutes a major threat to agriculture in California. The larvae eat fruit voraciously and almost indiscriminately, and the adults breed like, well, flies. Despite heroic attempts to eradicate the California Medfly, new infestations keep appearing in odd and unexpected places. The patterns of infestation are so bizarre that some members of the panel concluded that someone or some group of people must be purposely breeding and releasing Medfly larvae. This scenario might seem farfetched except for the fact that Tom Bradley, the mayor of Los Angeles, and various newspapers received letters during 1989 from a group calling itself the Breeders, which claimed to be spreading Medflies to protest California agricultural practices.
The threat that agricultural bioterrorism would pose is vast and carries with it the potential for severe economic disruption. One historical example illustrates this potential. From 1940 to 1942 the beehives of several European countries, including Germany, were decimated by an infestation of Nosema apis, a one-celled parasite that infects the digestive tracts of honeybees. Nosema apis is usually harmless, but occasionally, for reasons that are not entirely clear, it mutates into forms that are deadly. It was one of these deadly forms that ran rampant during the Second World War, not only severely curtailing honey production but also, because bees are the primary pollinators of many food plants, crippling crop yields. As Karl von Frisch, the great expert on bees, has noted, "During a time when food was in short supply, this failure of the bees was therefore a twofold catastrophe." Starvation has been a weapon of siege for as long as cities and states have existed. It is simply too optimistic to think that military planners and terrorist organizations have suddenly forgotten this fact.