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The Growing Threat of Biological Weapons

The terrorist threat is very real, and it's about to get worse. Scientists should concern themselves before it's too late

Steven Block

The Plague and Anthrax

Biological warfare is not a new phenomenon. The ancient Romans, and others before them, threw carrion into wells to poison their adversaries' drinking water. In the 14th century the Tatars catapulted the bodies of bubonic-plague victims over the city walls of Kaffa, a Black Sea port that served as a gateway to the Silk Road trade route. People inside the city soon came down with the disease, suggesting that the maneuver may have worked—but the tactic may have exceeded the Tatars' operational goals. Some of the city's inhabitants escaped in sailing ships, which happened to be infested with rats, carrying fleas infected with the causative agent of plague, the bacterium Yersinia pestis. The escaping ships entered various Italian ports that subsequently served as foci for the spread of the disease. Over the next three years, the bubonic plague—the Black Death—raged northward, wiping out nearly a third of Western Europe.

It was not until the 19th century that the microbial basis for infectious disease was understood. One of the first illnesses to be explained by the new germ theory was anthrax, an infectious disease common to sheep and cattle. Indeed, the primary architects of the germ theory??Robert Koch, Louis Pasteur and Joseph Lister??were instrumental in describing anthrax and its containment. Koch was the first to isolate and describe the anthrax bacterium (Bacillus anthracis). Pasteur developed the first animal vaccine against anthrax, which, together with Lister's ideas about antiseptic precautions, helped turn the tide against outbreaks of the disease.

Anthrax is only weakly communicable in humans and rarely causes disease, unless the bacterium comes into contact with the bloodstream through a wound (causing cutaneous anthrax) or is ingested in contaminated meat (resulting in intestinal anthrax). However, Bacillus anthracis has the ability to form resistant spores, which can remain viable for over a hundred years if kept desiccated and out of direct sunlight. Breathing in significant numbers of spores (typically estimated at about 10,000) can lead to inhalation anthrax in humans, which was historically called "woolsorter's disease" because spores were prevalent in the contaminated wool of sheep in 19th-century England. Inhalation anthrax is a very deadly disease in humans. Unless treated with large doses of a penicillin-type antibiotic within the first day or so of exposure it has a mortality rate in excess of 80 percent. This is to be contrasted with smallpox, which has a mortality rate of "only" around 30 percent. Only some filoviruses, such as Ebola, which cause hemorrhagic fevers, have comparable rates of mortality.

All of this suggests why Bacillus anthracis became the agent of choice for most biological warfare programs. Consider the properties of anthrax. It is convenient: Variants of the anthrax bacterium can be isolated worldwide (although not all possess equal virulence), and great quantities of spores can be readily prepared from liquid cultures. It is robust: Once desiccated and stabilized, hardy spores have a long shelf life and are well suited to weaponization in a device that can deliver a widespread aerosol. It is self-terminating: Airborne spores remain infectious until they fall to the ground, where most become inactivated by sunlight. It is effective: After inhalation the spores produce disease with a high mortality and morbidity. It can be contained: Anthrax is not very communicable, thereby reducing the risk that it will spread beyond the intended target. Moreover, a well-established vaccine exists that can prevent the onset of the disease, allowing it to be used safely by the aggressor. This is a two-edged sword, of course, since the vaccine may be available to the target population as well. For this reason alone, anthrax doesn't quite qualify as the perfect bioweapon.

There are certain other drawbacks to anthrax as a weapon. The number of spores that must be delivered to the lungs to produce the disease is quite high compared with some other infectious agents??it has been estimated that certain viruses and rickettsiae may communicate disease with just a single particle. Finally, for conventional anthrax, antibiotic treatment can be effective if administered quickly. Even so, of all the natural biowarfare agents, anthrax traditionally ranks near the top of everyone's short list.

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