Barry Kellman, Biological terrorism: Legal Measures for Preventing
Catastrope, 24 Harvard Journal of Law
and Public Policy 417-484, 425-446 (Spring 2001)(191 Footnotes Omitted)
Because a catastrophic bioterrorism attack has not yet happened, trying to understand the
phenomenon entails some speculation based on reasonable extrapolations both from the scientific
understanding of pathogens and from the social science understanding of terrorist behavior. There
has been only one notable effort to develop and employ biological capabilities for terrorist
purposes, which was by the Japanese cult Aum Shinrikyo.
Aum devoted vast sums of money, time, and considerable expertise to the task of making
biological weapons, but it was not successful. Before puncturing bags of sarin nerve gas on
Tokyo subway trains on March 20, 1995, killing twelve people and injuring more than 5,000, the
cult had sought to acquire a wide range of weapons, including biological weapons. In April 1990,
Aum attempted to attack the Japanese parliament with botulinum toxin aerosol. In 1992, Aum
sent a mission to Zaire to assist in the treatment of Ebola victims in order to find a sample of the
Ebola strain to take back to Japan for culturing purposes. In June 1993, the cult tried to release
poison at the wedding of the crown prince. Later that month, Aum attempted to spray anthrax
spores from the roof of a building in Tokyo. All these attacks were unsuccessful and resulted in
no casualties. The consequences might have been drastically different had the weapons been
The cult built weapons under the guidance of well-trained biologists and chemists. They created
a sophisticated biological research facility without attracting the attention of the Japanese or other
governments. When Japanese officials investigated Aum's compound after the 1995 attack, they
found large amounts of equipment indispensable to cultivating bacteria and viruses, peptone (a
substance used to cultivate bacteria), and books and materials on the production of botulism,
cholera, and dysentery. At Aum's site in Naganohara, officials found a four-story concrete facility
equipped with a "clean room" with specialized ventilation systems and a sealed room to protect
cultivated bacteria from leaking. In connection with these operations, Aum produced illegal drugs
for their own use and for sale to others.
In January 1995, an Oregon company sold Aum molecular modeling software that simulates
molecular experimentation without the need for actual laboratory experimentation. This software
is covered by export restrictions to countries such as China but not to Japan. Aum could have
used this software to test theoretical designs for toxins. In March 1995, Aum supporters
contacted a Missouri company that produces computer software for use in designing new
therapeutic drugs but that can also be used to research and develop biological toxins. Although it
harbored suspicions, the Missouri company installed software on a computer provided by Aum.
Five days before the Tokyo gas attack, authorities discovered three attaché cases containing a
small tank to hold liquid, a small motorized fan, a vent, and a battery. The cult had at least two
radio controlled drone aircraft, and they were seeking hundreds of small fans as well as thousands
of small serum bottles.
The Aum Shinrikyo experience raises several questions addressed in the remainder of this Part.
First, why would a terrorist use biological weapons? Second, what pathogens could or would
likely be used? And third, could an attack be concocted?
A. Why Attack with Biological Weapons?
Why would anyone use disease to cause mass death? How difficult is it to use biological agents
as weapons, assuming the motivation to do so? If biological weapons are used, what casualties
can be reasonably expected?
Biological weapons have three advantages from a terrorist's perspective. First, they (as well as
chemical weapons) offer an optimal death to cost ratio. Second, they are virtually undetectable
and can be handled with relative ease by properly trained and inoculated persons. Third, they offer
the potential for mass panic that may uniquely serve a terrorist's purposes.
1. Inflicting Casualties
If a terrorist wants to kill thousands of people, biological weapons merit serious consideration. A
nuclear weapon, by comparison, can certainly create far more devastation, but making a nuclear
weapon is far more difficult and expensive, and smuggling it poses a far greater risk of detection.
At the other end of the weapons spectrum, firearms are inexpensive and readily available, but they
have the capacity to kill only a few dozen people before being stopped. Explosives present more
technical obstacles than firearms, but offer the potential for inflicting far greater casualties. The
failed attempt to blow up the World Trade Center building and kill thousands illustrates the
difficulties inherent in this tradeoff. The calculus of terrorism, therefore, leads inexorably to
biological and chemical weapons. Comparatively, while chemical weapons are easier to make and
use, biological weapons are less detectable, less dangerous to the terrorist, and--except in a few
scenarios-- have greater killing capability.
Estimates vary widely as to the numbers of dead and sick from a bioterrorist attack. Projected
seven-figure casualty estimates, based on multiplying the quantity of pathogen necessary to kill an
individual, are flawed. Under this methodology, for example, a lethal dose of Type-A botulina
toxin can be prepared in concentrations of ten billion micro-organisms per gram; accordingly,
eight ounces is enough to kill every living creature on Earth. This arithmetic misleadingly assumes
that these doses will be equally and effectively disseminated. But most pathogens disseminated
among a large population would not be ingested at all and would die harmlessly from natural
causes. The pathogens that are ingested would tend to be concentrated in a fraction of that
population, and even some of these persons would, for various reasons, not get sick.
Nonetheless, there are reasonable scenarios involving dissemination of pathogens in confined
spaces that predict over ten thousand casualties; in extraordinary circumstances, casualties in
excess of 100,000 are not fanciful.
2. Non-Detectability and Manageability
Besides their capability to cause mass casualties, there are other good reasons (from a terrorist's
perspective) to use biological weapons. Pathogens are undetectable or nearly so. Lethal pathogens
may be attractive to foreign terrorist organizations or even rogue States seeking to cause
catastrophic injury to the United States without exposing themselves to reprisal. Pathogens can be
brought into the country by a single individual and can be smuggled through airports or customs
checks. Once here, they can be propagated into enormous quantities. Even their use is initially
undetectable. An epidemic can be initiated, and it may be days before symptoms are manifest;
even then, the attack may be mistaken for a natural outbreak. Terrorists could easily have
sufficient time to flee the scene of the attack, and perhaps the jurisdiction altogether, before law
enforcement officials learn that a crime has been committed. The time-lag between release and
effect on humans thus reduces the risks of a perpetrator being apprehended. Another contribution
to anonymity is that dissemination of pathogens need not leave identifying markers that could be
traced back to the perpetrators. No other weapon offers a comparable capability to inflict
catastrophic disruption anonymously.
Despite their disease-causing capabilities, some pathogens can be produced and handled safely
by persons who are properly equipped, knowledgeable of the risks, and perhaps inoculated against
the disease. Starting with a small seed culture, terrorists could easily generate a stockpile and can
work with it, carry it, and distribute it without undue risk. Some, but not all, pathogens have the
ability to reproduce in the target population. If sufficiently contagious, an attack would only have
to be against a small group (perhaps at an airport) who would then do the terrorists' work for
them by carrying it out to a wider population. No other weapon offers similar capabilities to
spread itself. Therefore, the problems of dissemination (discussed below) can be overcome to
some degree by creating a more potent agent.
3. Panic Potential
Arguably the greatest advantage of biological weapons is their ability to cause mass panic.
Bombing a large and heavily populated building is terrifying, as is releasing chemical weapons in a
confined space such as a subway, but these attacks are geographically limited. A biological attack
makes everyone vulnerable, and this insecurity is the terrorists' primary motivation. Moreover,
even if not empirically justifiable, humanity fears disease not only for its ability to kill but for the
horrifying way in which it kills. While we have no experience with a catastrophic terrorist attack,
memories of past epidemics incite fears of future outbreaks. Thus, even if a biological attack kills
only a relatively small number, it is likely to generate panic. This shredding of the fabric of the
community and exposure of society's vulnerability, perhaps on a global scale, is the incentive for
committing such heinous crimes.
Pathogens may appeal to domestic terrorists who have an anarchic or mystical sense that the
modern era is corrupt, excessively regimented, or materialistic. For those with a profound sense of
alienation or those motivated by a distorted sense of religious faith, disease has a unique Biblical
history suggesting that God has often inflicted a scourge on the sinful. Inflating the death toll may
be seen as performing a sacramental act, manifesting divine retribution that morally justifies mass
B. What Pathogens Might Be Used?
The Centers for Disease Control (CDC) lists thirty-six pathogenic agents, including seven
bacteria, thirteen viruses, three rickettsiae, one fungus, and twelve toxins.(1) Bio-engineered
variations of these agents, or development of new agents altogether, could expand this list.
1. Likely Pathogens
This Section briefly describes the agents most often cited as potentially weaponizeable and
briefly explains their relevant characteristics. It must be noted that no agent is perfect; a terrorist
must therefore choose among various characteristics, including:
• Pathogenicity of the agent (how likely the agent is to kill its victim): Agents can be chosen to
sicken, incapacitate, or kill; to spread from person to person or to affect only those initially
exposed; and to be susceptible or resistant to medical treatment.
• Degree to which the agent is contagious or infectious: The infectiousness of the agent is
directly correlated with the mode of weaponization. If the terrorist intends to spray dust an area
and infect via an aerosol cloud, then the likelihood of successful delivery is less than direct
injection. Therefore, a more infectious agent would be more desirable.
• Process of contagion and resistance to protective measures or cures: The terrorist will also
choose an agent that is known to be transferable or containable, depending once again on the
terrorist's targeted group. For instance, if the intent is to cause a widespread outbreak, an agent
that can be transmitted by coughing or contact with others would be more favorable than one that
cannot be transmitted by human to human contact. Further, agents have variable lengths of
incubation periods, some allowing ample time for vaccination once an outbreak has been
identified. Also, agents differ in the length of time between the onset of symptoms and death.
• Degree of lethality (how many people are likely to be affected): In choosing the appropriate
agent to execute the mission, the terrorist likely would consider the lethality of the agent. For
instance, agents differ in incubation stages, some acting on their hosts quickly and others not
showing signs for several days. Moreover, agents differ in their contagion capabilities. Therefore,
when the intent is to indiscriminately pass the illness to a large number of people over a period of
time, a less lethal but highly infectious agent may be chosen.
• Potential risk to the terrorist himself: The terrorist, through his knowledge of the agents and
their production methods, may consider the risks of handling that the agent poses to his health in
all the steps until it is disseminated. Those whose scientific proficiency bolsters their confidence in
handling pathogenic agents may be more willing to weaponize highly pathogenic agents as
compared to those who are wary of the unknown. It may be very important that there is an
available vaccine with which the terrorist may vaccinate himself.
The smallpox virus is among the most dangerous organisms that might be used by bioterrorists.
It is virulently contagious, often fatal, and spread through inhalation. Smallpox was responsible
for hundreds of millions of fatalities before widespread vaccinations were thought to have
eradicated it. In 1986, the Executive Committee on Orthopox of the World Health Organization
unanimously decided to destroy the last strains of smallpox left in the world except for two
samples in Moscow and Atlanta. However, unsubstantiated but highly disturbing reports from
Russia suggest new concerns. This is especially frightening because health authorities, believing
the disease to have been virtually eradicated, have discontinued vaccination programs, leaving
current populations highly vulnerable to a terrorist attack using smallpox.
Anthrax (Bacillus anthracis) is often mentioned as the biological agent of choice. Anthrax is a
spore that, if inhaled even in extremely low quantities, is nearly always fatal unless the patient is
quickly given huge quantities of antibiotics. Ingestion leads to fatigue, coughing, fever, and chest
pains; death comes within twenty-four to thirty-six hours. Anthrax has important virtues from a
terrorist perspective. It occurs naturally in the soil. Herbivorous animals such as sheep or goats
ingest spores while grazing. Seed cultures of the spores can be taken from samples of the wool or
skin; taking more samples increases the likelihood of success. Only small samples would be
needed, perhaps no larger than a postage stamp. Although anthrax is more common among
Caribbean and Eastern Mediterranean countries, it is not impossible to find infected animals in the
United States. As a weapon, the primary virtue of anthrax is its lethality; some experts assert that
as little as a single gram, efficiently distributed, could kill more than one-third of the United States
population. Another advantage is that it is an endospore and thus highly resistant to humidity,
pressure, or temperature. Moreover, anthrax can be easily propagated. For these and perhaps
other reasons, anthrax has been by far the most often pathogen allegedly used in the United
States, although most if not all of these alleged uses were hoaxes.
Anthrax, however, has various disadvantages as a weapon. The fact that it is a spore and hence
large relative to other agents means that it is difficult to aerosolize for weapons purposes, and,
once released, falls rapidly to the ground, thereby diminishing the opportunity for inhalation.
Furthermore, anthrax is not contagious except by direct contact. To kill many people would
therefore require widespread dissemination. There is a licensed vaccine which, although the
subject of considerable controversy in connection with its use during the Gulf War, can be
effective if administered soon after exposure. This vaccine would, of course, enable a potential
terrorist to handle anthrax without risk of infecting himself.
c. The Plague
Plague (Yersinia pestis) is a contagious bacterium. Only slightly less lethal than anthrax, it is also
naturally available and can be scraped from dead animals. In North America, plague is found in
certain animals and in their fleas from the Pacific Coast to the Great Plains, and from
southwestern Canada to Mexico. It is more difficult to grow than anthrax, requiring a blood agar,
but not so difficult as to preclude its potential weaponization. A licensed vaccine that would allow
a terrorist to protect himself is available. However, this vaccine is used in animal experiments and
will provide no protection against the aerosol exposure; a terrorist who chooses an aerosol route
of dissemination would have to immediately take the antibiotic doxycycline. Unlike anthrax,
plague is highly communicable; an infected individual may spread infection by coughing. Its
capability to lead to an epidemic may be an advantage to someone seeking to generate mass
havoc, but it may be a disadvantage to someone planning a more strategic strike. In contrast to
anthrax, plague bacteria have the disadvantage of being subject to environmental stress,
d. Haemorrhagic Fevers
Rift Valley Fever (RVF) is a viral disease prevalent among livestock. The virus is spread by
mosquitoes to animals. Infected animals then become new hosts for other mosquitoes that in turn
become additional vectors for transmission. These mosquitoes can then infect humans. RVF
victims tend to experience symptoms associated with a mild illness such as fever, dizziness, and
back pain. In some people, the illness can progress into hemorrhagic fever, encephalitis, or ocular
disease, but most patients recover from exposure within a few days. A terrorist's mishandling may
lead to unintentional exposure, with no known treatment.
Marburg Hemorrhagic Fever affects humans and other primates in very localized areas. Like the
plague, the virus is highly infectious. Humans can contract the disease from handling monkeys,
from droplets of body fluids, or contact with contaminated people or other sources of infectious
blood or tissues. Symptoms appear five to ten days after exposure. Death ensues rapidly. This
virus may appeal to the potential terrorist for its 25% mortality rate, but knowledge of the virus
and proper handling are necessary to prevent risk to oneself.
The ebola virus is known for its horrific symptoms: vomiting, chest pain, and bleeding from
virtually every orifice. The disease is spread through close personal contact with an infected
victim. Transmission has also been known to take place through hypodermic needles. The ebola
virus is similar to the Marburg virus but has a lower infection rate. Humans are susceptible to
several different strains; the more lethal strains are the less contagious.
Tularemia (Francisella tularensis) is an extremely lethal bacterium spread by insect bites from
rodents to humans. A virulent form (fatality rate of approximately 5%) is endemic in much of
North America and can be obtained from dead animals; a pneumonic form, which would result
from an intentional release, would likely have a greater mortality rate. Propagation would require
special media as tularemia does not typically grow in standard blood cultures. It is not transmitted
person-to-person, eliminating the possibility of epidemic. Treatment is typically effective by
common antibiotics within seven to fourteen days of infection, making treatment and containment
by public health authorities possible. Moreover, like plague, it is subject to environmental stresses.
f. Venezuelan Equine Encephalitis
Venezuelan Equine Encephalitis (VEE) is a mosquito-borne virus. A large controlled mosquito
population could feed on an infected animal and become the vector to transfer the virus to
humans. Susceptibility to this disease is nearly 100%; however, its mortality rate is less than 1%,
making it an unlikely choice for a weapon. An infected human remains infectious for mosquitoes
for at least seventy-two hours after symptoms, enabling secondary spread of the disease. Infected
individuals who do not seek treatment may progress into encephalitis, which is marked by
convulsion, coma and paralysis. A human vaccine is available through USAMRIID.
Ricin is an inanimate protein toxin that may be readily produced from castor beans. It acts as a
cellular poison that is lethal either through inhalation or through epidermal absorption. A tiny
quantity on the skin rapidly causes death. Ricin may be used to poison water or foodstuffs or lace
injectiles. Ricin has a long record of use by assassins because the victim need only be poked by an
object coated with the toxin. If ricin is inhaled, fever, coughing, and nausea occur within eight
hours and death ensues within thirty-six to seventy-two hours. Notably, there is no treatment;
once a victim is poisoned, death will follow. There is no vaccine, so a terrorist would have to be
extremely sophisticated to avoid suicide. Since it is non- contagious, it has no ability to provoke
an epidemic, yet it may be the most easily disseminated pathogenic agent and therefore one of the
most effective means of committing murder.
2. Choosing the Appropriate Pathogen
No single agent is ideal for terrorism. A terrorist must make choices depending on what he is
trying to accomplish as well as his level of technical knowledge and equipment.
If the goal is to murder an individual or small group of people, ricin may be uniquely suitable.
Ricin is easily produced from widely available castor beans. Because it kills by epidermal contact,
it is likely that the murderer will remain anonymous. However, there is no shortage of guns,
knives, conventional poisons etc. available to the terrorist who wishes only to kill a small number
of people; producing ricin may not be worth the time and risk.
If the terrorist's goal is mass murder, anthrax deserves its reputation as perhaps the most feared
biological weapon. It is readily available. Disseminated in a closed, positive air pressure
environment, anthrax could get into the lungs of most people in that environment. By the time
symptoms become obvious, it would be difficult, even with a full commitment of health care
resources, to prevent a high number of deaths. In other settings, however, the difficulties of
suspending anthrax outdoors and the unlikelihood of it spreading from one victim to another
render it a poor open-air, urban- devastating weapon.
If the terrorist's goal is contagion, plague is almost as readily available as anthrax and is
contagious, although it is less resilient to environmental stresses and more difficult to cultivate.
More esoteric are viruses including encephalitis or any of the extremely deadly hemorrhagic
fevers. These viruses are far more difficult to obtain, and the knowledge of how to propagate
them safely is far more limited. Moreover, as these viruses are not available domestically, the
terrorist would have to go to some other part of the globe and bring at least some agent through
customs, thereby risking detection. The organisms of brucellosis are difficult to grow, but are
highly infectious and relatively stable for aerosolization. The tularemia organism is also extremely
infectious; however, it is difficult to grow and is delicate when disseminated.
If the terrorist's goal is a weapon of mass destruction, smallpox has attributes of contagion and
lethality that are unmatched by any other natural agent. However, smallpox is available, if at all,
only from unsecured Russian laboratories. To obtain and transport it into the United States would
entail an organized conspiracy more akin to an act of war than an act of terrorism. Sophisticated
bio-engineered agents, whether animate or toxin, are similarly effective but require foreign
assistance in order to be obtained. The good news here is that using biological agents as a weapon
of mass destruction seems to be well beyond the capabilities of domestic hate groups or the likes
of a Tim McVeigh or Ted Kaczynski ("The Unabomber").
C. Devising the Attack
How difficult it is to make biological weapons and how much sophistication is required are
matters in sharp dispute. According to some experts, medical or microbiology students could
prepare an agent without endangering themselves. But making that agent into a weapon by
aerosolizing it requires considerably greater sophistication. Many experts believe that the
difficulties of executing a mass biological attack explain why such a successful catastrophic attack
has not yet occurred. Persons having extraordinary technical knowledge may be able to overcome
problems of deficient resources and equipment, but there is a negative correlation between
capability to use pathogens and a motivation to cause mass casualties.
1. Means of Acquisition
A seed culture could be obtained from a legitimate facility either by purchasing it or stealing it,
from the natural environment, or by importing it. Purchase of pathogens was once not difficult,
but controls have recently been significantly tightened, as will be discussed at length below. As
discussed below, the stealing of agents raises serious problems, including alerting law enforcement
authorities to the risk of an attack. Therefore, access to these agents may require the services of
someone affiliated with the laboratory or facility.
The most likely means of acquiring pathogens are from a natural or a foreign source. Either of
these means, as distinct from buying or stealing pathogens, is virtually unstoppable. Within the
United States, agents such as anthrax and plague and tularemia as well as variety of toxins, can be
obtained from dead animals or vegetable matter. Resort to this method minimizes the risks of
detection as well as the financial cost. However, identifying a strain that can be effectively
weaponized and then proceeding to weaponize it requires considerable sophistication as well as
equipment. Procurement from a foreign source is a virtually foolproof solution to the task of
acquisition, although smuggling the material into the United States poses risks of detection.
Unless the agent is already weaponized (which would increase the danger and detectability of
smuggling it), it would have to be weaponized here. In that respect, obtaining an agent from a
foreign source poses problems similar to obtaining it from a natural source, although the agent is
likely to be of a higher quality.
2. Means of Production
Once the agent has been obtained, it must be cultured. The difficulty in producing enough of the
agent to create a weapon may present an important limitation to terrorism, because some methods
may be too advanced for terrorists. Moreover, agents are fragile; production would require
favorable conditions. For instance, the terrorist would need the appropriate media, the right
temperature, pressure and atmospheric conditions, and the ability to maintain this environment for
the necessary time for the particular agent. For bacteria, growth and production imply taking a
small isolate (perhaps a test tube) and growing a large quantity that can be used in a weapon. The
actual quantity of material required to produce an effective weapon depends on many factors, not
least of which is the strain's virulence. Although some organisms are known to cause disease when
infected with fewer than 100 cells (Pseudomonas), higher concentrations increase the chance of
infection. Therefore, large volumes of highly concentrated material are required for a biological
The scientific proficiency required to culture an agent is a factor in agent selection. Growth and
media requirements and techniques for production for pathogenic microorganisms are easily
researched. The pathogenesis of these organisms has led to intensive study of growth
characteristics and requirements, which are now well understood and published. However,
obtaining the growth media used in traditional research, as well as the clinical setting, presents a
significant hurdle in creating a biological weapon. For instance, Yersinia
pestis, the bacterium that
causes plague, is difficult to grow on any media other than blood agar.
3. Means of Dissemination
The means of delivery will depend on the number of people the terrorist seeks to reach and his
ability to successfully weaponize the agent. For instance, dissemination by aerosolization, as
opposed to delivering a sealed box of dry powder agent leading to infection if inhaled, requires
knowledge and skill with regard to how to minimize the particle size of the agent and spread it in
a fine cloud. Yet the requisite technology, laboratory facilities, and aerosolization devices are
within the grasp of even the weakest countries.
Commentators differ as to the difficulty of disseminating biological agents. Biological agents
can be disseminated individually through inanimate objects such as sticks, dusters, or projectiles.
But if one seeks to spread disease to many people, the more common methods of dissemination of
biological agents include aerosol delivery, dry-powder delivery, spraying, infecting food and water
supplies, and introducing insect or animal vectors. The bioterrorist must choose an agent that has
infectious capabilities but does not kill its host quickly. The fragile nature of the agents themselves
can impede any dissemination effort; preparing and preserving the agent before dissemination can
affect its ability to survive spraying and cause disease. Mechanical stresses and exposures to air,
humidity, and ultraviolet light rapidly kill many microorganisms.
These considerations, in turn, will also contribute to the chosen route of dissemination. For
instance, living microorganisms may enter the human body by an aerosol route, where they invade
the respiratory tract, enter the bloodstream and lymphatic system, and then initiate infection;
anthrax is not really infectious except by the aerosol route. By contrast, toxins affect people
through direct exposure; they have no infectious characteristics but rather must be ingested,
injected or inhaled.
a. Injection or Direct Poisoning
Almost all of the known incidents of hostile use of pathogens or toxins have involved direct
injection or poisoning of an individual. This method of dispersion, referred to as "point source,"
occurs where the enemy spews a biological agent directly on the target. Ricin-tipped umbrellas
have been used for clandestine espionage and counter-intelligence, and popular novels have
illuminated the implications of murder-by-biology. These incidents are cited as evidence of how
easy it is to make lethal biological agents, but there are prodigious technical differences between
homicide and mass catastrophe. As earlier stated, guns are remarkably easier and cheaper to
obtain and use.
b. Contamination of Foodstuffs or Potable Liquids
The easiest way to distribute pathogens is to spread them on foodstuffs. Most examples of
successful biological terrorism have involved spreading food-borne diseases (e.g., salmonella) on
openly accessible food sources such as salad bars. This type of attack is virtually impossible to
prevent once the terrorist has developed the agent and has obtained access to the food source.
Yet this type of attack is not likely to cause a catastrophic number of injuries; indeed, experience
with this type of attack suggests that casualties are more likely to number in the dozens than the
thousands. The most infamous known event of this type was in 1984 when the Rajneesh cult
outside of Antelope, Oregon, poisoned 750 people with salmonella at local salad bars. Attacks
through bulk foodstuffs or beverages have been discussed, but most experts believe that such a
mass attack is unlikely.
Contamination of water supplies is considerably more difficult in countries which have efficient
water purification systems (such as the United States) because of the extraordinary quantities of
pathogens necessary and because filtration and chlorinated purification systems would likely kill
the agent. Notably, Chicago-area neo-nazis were arrested in 1972 with thirty to forty kilograms of
typhoid bacteria for use against water supplies. That a few college students could cultivate this
disease in a school laboratory provoked considerable concern, but their selected organism would
have been readily destroyed by normal chlorination. This distribution method, however, could be
effective in less-developed regions.
c. Aerosol Delivery
A terrorist employing biological weapons for a large-scale attack with many casualties will most
likely distribute pathogens as an aerosol through airborne transmission. Experts differ as to how
difficult aerosolization is likely to be. While most experts recognize the ready availability of
aerosolization equipment (discussed below), there is considerable difference of opinion as to the
level of expertise needed to produce an aerosol generator capable of weaponizing pathogens.
Outside aerosol delivery highlights contrasting opinions. An effective delivery system must have
two major attributes. First, the delivery system needs to expel the agent efficiently from its
container so that it will travel to potential targets. Second, assuming the agent attacks through the
respiratory system, the delivery system must produce small particles that will be retained on
inhalation. Ranges of one to ten microns are required because larger particles settle out of the
atmosphere rapidly and are not inhaled. Paint spray devices are ineffective because of their large
particle size. Also because of the necessity of small particle size, a terrorist employing agricultural
spraying as his method of dissemination will have to address the problem of decreasing the
particle size. Agricultural sprayers expel droplets of a size range that will fall onto the crops. By
contrast, smaller particle sizes are necessary to produce an aerosol cloud which will suspend
above the surface level.
Even if the terrorist can accomplish this successfully, a hardy agent is still required to survive the
expulsion from a sprayer long enough to infect the intended targets. Outdoor aerosol delivery of
biological weapons is acutely sensitive to weather conditions, the quality of the dispersal system,
and the characteristics of the agent used, making aerosol dissemination of all but a few hardy
species technologically challenging. The stress of the aerosolization process itself can kill a large
portion of the pathogen; atmospheric conditions such as moisture, sunlight, smog, and
temperature changes can take an enormous toll. A nighttime dissemination under stable
meteorological conditions would improve chances of success. A cloud released to drift over a
densely populated urban area during a mild winter night would probably be most effective; a light
wind to prevent the aerosol from settling and an inversion layer to confine the cloud to lower
altitudes would aid dissemination.
Somewhat more effective is aerosol dissemination in an indoor setting such as by gaining access
to the air circulation system of an office building or public arena. The U.S. Army demonstrated
the effectiveness of this delivery system by releasing harmless bacteria into New York City
d. Animal and Insect Vectors
Vectors are normally insects that carry a host of different infectious agents, but a vector can be
any creature that transmits an infectious agent to humans when it bites or touches a person. The
infectious agent may be injected with the insect's salivary fluid when it bites, or an insect may
regurgitate material or deposit feces on the skin that enter a person's body, typically through a bite
wound or skin broken by scratching or rubbing. Once the agent is within the vector animal, an
incubation period follows during which the agent grows or reproduces, or both, depending on the
type of agent. Only after this phase is over does the vector become infectious.
A highly contagious pathogen could be propagated in a dead animal, and then large numbers of
insects could be exposed to that carcass in a confined space, collected, and then released in a
population center. Allegedly, the Soviet Union had researched this dissemination method, but
there is scant evidence that terrorists have mastered it. More recently, Cuba accused the United
States of committing a biological attack by distributing disease- carrying insects from aircraft.
Using insect vectors overcomes the difficulties of aerosolizing pathogens, but the use of insects
is necessarily unreliable. Significantly, because only a few pathogens (notably the tropical viruses)
are transmittable through this method, a terrorist would reduce options by using insects. To be
effective, a highly contagious pathogen must be selected, raising the risk of self- contagion.
4. Assessing the Risk
It would verge on pure speculation to assert that the risk of a particular biological attack is
significant or not. Conversations with U.S. government officials suggest that staging a biological
attack is far easier than using a nuclear device, even a crude one. But there is no way to confirm
or measure this risk. Decisions on appropriate policies must be made, therefore, in a condition of
some uncertainty. Yet it should be noted that the direction of biological understanding renders
current estimates somewhat irrelevant as to future capabilities. Even sophisticated biologists in the
1980s would have been hard pressed to predict the quality and magnitude of today's
bio-engineering; implementation of policies to address threats are likely to follow a somewhat
1. See 42 C.F.R. § 72, Appendix A (2000)