An Evaluation of anthrax as a weapon of bioterrorism

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An Evaluation of Anthrax as a Weapon of Bioterrorism

Introduction

Since September 11th, terrorism has featured regularly in the media causing widespread alarm. Since the postal attacks in the winter of 001, in which Bacillus anthracis spores were delivered by mail to targets of terrorism, attention has turned to the possibility of terrorist attack using bioweapons.

Bacillus anthracis The Organism




Bacillus anthracis spores, the initial infective agent of the disease anthrax are 1-�Ým by 0.5-1�Ým in size(). Once implanted the spore germinates into the vegetative cell, a gram positive, facultatively anaerobic bacterium(1). These non-motile vegetative cells are 1-8�Ým by 1-1.5�Ým in size() and secrete three toxin components lethal factor (LF), oedema factor (ED), and protective antigen (PA)(1) (see fig1).

1) Bacillus anthracis )

EF PA LF

)

Anthrax The Disease and its Treatment

The disease is exhibited in three forms in humans. The most common form is cutaneous anthrax. Spores penetrate the skin via a wound, germinate and cause a temporary disfiguring oedema(7). This is harmless unless the oedema blocks an airway but has been known to lead to anthrax meningitis in some cases(1). The most morbid form is inhalational or pulmonary anthrax, which is fatal in approximately 0% of cases(7). The third, rarest form of the disease is ingestional anthrax, which is exhibited gastro-intestinally or oropharyngeally(1). This occurs due to ingestion of meat from an infected animal. This form of the disease is fatal in around 50% of cases(7).

The vaccine employed in the USA is an inactivated cell free product, which is 0% effective for 1- years. This is currently administered to those in the military and high-risk members of the US postal service().

B.anthracis is sensitive to a range of antibiotics, such as penicillin, ampicillin, tetracycline, erythromycin, chloramphenicol, oxacillin, streptomycin(8), vancomycin, rifampin, chloramphenicol, imipenem, clindamycin, clarithomycin. Ciproflaxin or doxycyclin, along with one or two other antimicrobial agents are administered prophylactively for 100 days after suspected exposure to anthrax(). The use of antibiotics has promoted growth of strains resistant to quinolones (e.g. ciproflaxin) and macrolides (e.g. erythromycin)(10). The value of post exposure vaccine administration has been shown to have positive value as it initiates an immune response(11).

The Production and Employment of Bacillus anthracis As a Weapon of Bioterrorism

Anthrax was tested in the UK in 14 when small bombs containing B.anthracis spores were detonated on the surface of the Scottish island of Gruignard. Sheep were tethered near the test sites and number of them died from the pulmonary infection(1). The soil on the Island remained contaminated up until the early 180s.

Testing of all biological weapons was prohibited under the Biological Weapons and Toxins Convention (17) signed by most countries including Iraq and the USSR. Iraq went on to weaponize and produce enough anthrax to attack Iran and the Kurdish population(7). An accidental aerosol release of anthrax spores in Sverdlovsk in the former USSR resulted in 7 cases and 68 deaths(1).

Some autonomous terrorist organisations are capable of attack using anthrax as a weapon. The Japanese terrorist group Aum Shinrikyo have dispersed aerosols of anthrax throughout Tokyo on numerous occasions but did not succeed in infection().

To perform a terrorist attack, a terrorist must first obtain a suitably virulent strain of anthrax, such as the Ames strain of anthrax used in the recent postal attacks. The terrorist may obtain the organism from a number of sources. One possible source would be an infected animal carcass from a region in which the disease is still largely present, such as Iran. The organism must then be cultured on a suitable medium. A medium containing thallous acetate and EDTA is a medium selective for B. anthracis as EDTA chelates an essential cation. B.anthracis can utilise thallous acetate as a replacement while Bacillus cereus (a closely related bacterium) can not(14). Enough B.anthracis spores for a small-scale postal attack (only a few litres) may be cultured in a regular kitchen(7). To cause inhalational anthrax, the product must be milled into a fine enough powder to become airborne on opening of the package at its destination.

Weapons-grade anthrax, which is milled into a very fine powder, absent of the sticky material difficult to eliminate with only basic equipment, may be obtained by theft from research installations, or purchased from a rogue nation such as Iraq or rogue elements within a nation such as the Russian Mafia.

A large-scale terrorist attack would be extremely difficult but not impossible. Detection by the authorities must be avoided, sufficient funding must be found. Getting the spores airborne is also difficult, as security regarding the procurement of an aeroplane for any purpose has tightened. Also, meteorology must be considered. Airborne spores may not travel upwind. High humidity decreases the time for which the spores remain airborne(1).

If 100kg of anthrax was released over Washington DC, the 10,000 to million fatal cases are predicted. This matches the effects of a hydrogen-bomb attack().

Escherichia coli has been cloned containing the plasmid encoding the lethal anthrax-toxin components. They produced less toxin than B.anthracis and did not excrete the product(14). This technique could be employed to produce large amounts of lethal toxin for felonious uses. Other organisms could be investigated as more suitable candidates for genetic manipulation to produce the toxin.

Anthrax Compared with other Possible Agents of Bioterrorism

Infective Agent. Predicted number of persons infected. Predicted number of persons killed.

Anthrax (Bacillus anthracis) spores 50 000 100 000

Plague (Yersinia pestis) bacteria 150 000 6 000

Tularemia (Fracisella tularensis) bacteria 50 000 1 000

A number of other organisms or biologically derived substances may be considered as potential agents of bioterrorism. Smallpox causing variola virus is possibly the most feared of these. The disease is extremely infectious. The infectious dose is only a few virions(15), while 500 to 55000 inhaled anthrax spores are required to cause pulmonary anthrax(). Secondary transmission of smallpox is possible via contact or droplet-infection(15), while anthrax finds a biological ¡§dead-end¡¨ in humans(1).

There is also no safe treatment for smallpox. Vistide (cidofovir) is thought to be useful but its use promotes renal failure(16). Once contracted, smallpox is around 0% fatal, while pulmonary anthrax is around 0% fatal once infected. Anthrax spores are also more persistent in the environment. Smallpox is also very difficult to obtain as it only remains in two laboratories in the world, one in the USA, one in Novosibersk in Russia(16). It is alleged that Russia has produced and weaponized smallpox for use in ballistic missiles(15).

Botulinum toxin is another agent employed by the Aum Shinrykyo group in its attacks around Tokyo(). Derived from Clostridium botulinum, an easily obtainable, soil-dwelling bacterium, it is the most poisonous substance known to humankind. The lethal inhaled dose is less than 1�Ýg. An aerosol release is predicted to kill 10% of people to 0.5km downwind. Iran, Iraq, Syria and North Korea have weaponized botulism toxin(17).

Yersinia pestis causes potentially fatal pneumonic plague. Secondary spread is possible, as in smallpox. There is no vaccine available against Y. pestis and some antibiotic-resistant strains exist(18).

Francisella tularensis is one of the most infectious known bacteria. It causes tularemia, which is fatal to a lesser extent than inhalational anthrax(1) (as shown in table 1)

Conclusion

B.anthracis is indeed a potentially potent weapon of bioterrorism. Each agent of bioterrorism mentioned above has factors such as availability, infectivity, incidence of secondary infection, and fatality of the disease. Anthrax compensates for its relatively low infectivity and lack of secondary infection, by its availability, the fatality of the disease, and the persistence of the spore in the environment, which can be up to sixty years in soil(0). None of the other organisms mentioned persist in the environment for any significant length of time. The widespread panic among civilians and costs to the USA government in prevention (tightened security, development and production of vaccines and antibiotics) is the first significant victory to potential bioterrorists.

As terrorist organisations grow (even some countries, such as Iraq, are regarded as ¡¥terrorist states¡¦) the threat of large-scale attack, using anthrax as a bioweapon, grows concomitantly.

Word Count 1 words

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