Botulinum toxin is a neurotoxin produced by the bacteria Clostridium botulinum. The bacteria is an anaerobic (doesn’t require oxygen to grow), gram-positive (contains peptidoglycan in its cell wall), spore-forming rod found on plants, in soil, water and the intestinal tracts of animals. C. botulinum has eight antigencically distinguishable exotoxins (A, B, C1, C2, D, E, F, G) some of which have commercial and cosmetic application but others of which are considered to be the most dangerous poison on Earth. Botulinum toxin-A is popularly known as Botox and is used to reduce facial wrinkles and aging effects, but its closest neighbor Botulinum toxin-B can be harnessed to create pathogenic disease outbreaks across populations.
All serotypes of botulinum are single polypeptide chains with a molecular mass of about 150 kDa and a high degree of amino acid sequence homology. The polypeptide chain contains and heavy (H) and light (L) chain which play a crucial role in its pathogenesis[1]. Botulinum’s toxicity is orchestrated through its interference in neural transmission by blocking the release of acetylcholine at four different sites in the body: the neuromuscular junction, autonomic ganglia, postganglionic parasympathetic nerve endings and postganglionic sympathetic nerve endings[2]. Acetylcholine is the principle neurotransmitter in neuromuscular junctions which makes its inhibition result primarily in muscle paralysis .The heavy (H) chain binds irreversibly to the high affinity receptors on neurons allowing the toxin-receptor complex to enter the cell via endocytosis which then allows the light (L) chain to interact with various surface proteins to prevent fusion of acetylcholine vesicles with the cell membrane[3].. The initial symptoms begin with acute weakness of muscles causing difficulty in speaking, swallowing and blurred vision. This followed by flaccid paralysis beginning at the muscles in the head and throat and can eventually cause death from respiratory muscle paralysis[4].
Because of the speed and potency with which Botulinum strikes the body, it is considered one of the most toxic poisons known to humans. It’s estimated that even a single gram of pure crystalline toxin evenly dispersed and inhaled could kill as many as one million people[5]. The estimated lethal dose for a 200 pound person is around 0.9 – 1.2 micrograms by inhalation and approximately 90 micrograms by oral ingestion with symptoms appearing as quickly as 2 hours to as late as 8 days. In its solid form it is a white crystalline solid and in its liquid form it is colorless and odorless. Because the toxin is a protein, it is sensitive to heat and denatured at temperatures above 80 C (176 F) after 10 minutes[6].
Because of its extremely high toxicity (100 times more toxic than sodium cyanide), Botulinum toxin has been at the top of bioweapon candidate agents. C. botulinum is easy to grow in large quantities and able to be stored at incubation without much technical sophistication. Weaponizing botulinum would be a complex, multi-stage process where in the final stage the toxin would have to bind to a finely powdered material like bentonite or silica gel[7]. This binding allows the bacteria to form a stable aerosol vehicle for dissemination.
Terrorists have already attempted to use botulinum as a bioweapon. On at least 3 occasions between 1990 and 1995, the Japanese cult Aum Shinrikyo used aerosols to disperse the bacterial agent in Tokyo and on US military installations, but these attempts failed due to deficient aerosol-generating equipment and no one was killed[8]. The group acquired their C. botulinum from soil that they had collected in northern Japan. While non-state actors like Aum Shinrikyo have been unsuccessful, state actors have long been developing botulinum toxin as a bioweapon. In the 1930s, Japan’s government developed Unit 731, a bioweapons research complex, to test the effect botuliun had on Chinese, Korea and American prisoners it captured in the 1930s. The United States produced botulinum toxin during World War II out of fear that Germany had done so already (which they had). In fact before the D-Day invasion, over a million doses of botulinum toxoid vaccine were administered to Allied troops[9]. Even though Iraq and the Soviet Union were signatories to the 1972 Biological and Toxic Weapons Convention, both produced it for use as a weapon. Former senior scientists of the Russian civilian bioweapons program admit that botulinum toxin was tested at the Soviet site Aralsk-7 on Vozrozhdeniye Island in the Aral Sea[10]. After the demise of the Soviet Union, thousands of scientists employed by its bioweapons program have been recruited by nations attempting to develop biological weapons, specifically botulinum toxin, including Iran, North Korea and Syria[11]. After the Gulf War in 1991, Iraq admitted to having produced 19,000 liters of concentrated botulinum toxin with about 10,000 liters loaded into military weapons. The 19,000 liters to this day are not entirely accounted for and constitute more than three times the amount needed to kill the entire human population by inhalation. Amongst the range of biological weapons that Saddam’s Iraq had developed it chose to weaponize more botulinum toxin than any other agent. [12]
Analysts now downplay the potential for botulinum to be used as a bioweapon because of constraints in concentrating and stabilizing the toxin for aerosol dissemination[13]. The flaw in these analyses, however, is that they pertain only to military use in immobilizing an opponent rather than release of the agent in a civilian population. It’s estimated that a point-source release could incapacitate or kill 10% of persons downwind from the initial release which could wreak havoc in a populated civilian setting such as a subway transit or sports arena[14]. More dangerous than aerosol dispersion though would be the use of the toxin through the contamination of food which could result in widespread epidemics. Terrorists generally consider these “soft” targets, since they are almost impossible to guard at all times. Contamination of the food supply could come through spraying the agent on fruits and vegetables or through processed foods like dairy products or through hamburger and canned meats.
In order to recognize a biological attack from botulinum, there would have had to have been an outbreak with a significant number of incidents of flaccid paralysis all stemming from one geographic location. Once recognized, treating those affected and containing the spread can be very difficult. For some symptoms of botulinum infection do not appear for 8 days meaning they could inadvertently spread the toxin amongst family, co-workers etc before showing any signs[15]. Once an individual begins to show signs treatment would include breathing assistance and possible intubation, botulinum anti-toxins and a toxoid vaccine[16] which may or not be successful depending on the severity of the infection on the body.
Given that much of Iraq’s arsenal of weaponized botulinum toxin has been unaccounted for and thousands of bioweapons trained scientists from the Soviet Union have spread out across the globe, it is not hard to imagine that terrorist networks and perhaps even state actors have acquired strains of weaponized botulinum. While the current struggle may still be with efficient aerosol dispersal deign, there are more vulnerable targets today than there have been in the past. Terrorists could easily target today’s vast supply chain of globalized food export where areas of the marketplace are unregulated and where a number of middlemen control the shipping process. With these risks, the United States ought to have emergency response and hospitals equipped with all the proper medications to be able to swiftly and efficiently deal with an outbreak of botulinum toxin.
[1] Arnon et al, “Botulinum Toxin as a Biological Weapon – Medical and Public Health Management”, 2001, http://www.bt.cdc.gov/agent/botulism/botulismconsensus.pdf
[2] Nigam, PK and Nigam, Anjana, “BOTULINUM TOXIN”, Indian J Dermatol. 2010 Jan-Mar; 55(1): 8–14.
[3] Hanson, Doug Phd. “Botulinum Toxin: A Bioterrorism Weapon”, April 1st, 2004, http://www.emsworld.com/article/10324792/botulinum-toxin-a-bioterrorism-weapon
[4] Arnon et al, “Botulinum Toxin as a Biological Weapon – Medical and Public Health Management”, 2001, http://www.bt.cdc.gov/agent/botulism/botulismconsensus.pdf
[5] Nigam, PK and Nigam, Anjana, “BOTULINUM TOXIN”, Indian J Dermatol. 2010 Jan-Mar; 55(1): 8–14.
[6] Nigam, PK and Nigam, Anjana, “BOTULINUM TOXIN”, Indian J Dermatol. 2010 Jan-Mar; 55(1): 8–14.
[7] Arnon et al, “Botulinum Toxin as a Biological Weapon – Medical and Public Health Management”, 2001, http://www.bt.cdc.gov/agent/botulism/botulismconsensus.pdf
[8] Arnon et al, “Botulinum Toxin as a Biological Weapon – Medical and Public Health Management”, 2001, http://www.bt.cdc.gov/agent/botulism/botulismconsensus.pdf
[9] Arnon et al, “Botulinum Toxin as a Biological Weapon – Medical and Public Health Management”, 2001, http://www.bt.cdc.gov/agent/botulism/botulismconsensus.pdf
[10] Nigam, PK and Nigam, Anjana, “BOTULINUM TOXIN”, Indian J Dermatol. 2010 Jan-Mar; 55(1): 8–14.
[11] Nigam, PK and Nigam, Anjana, “BOTULINUM TOXIN”, Indian J Dermatol. 2010 Jan-Mar; 55(1): 8–14.
[12]Arnon et al, “Botulinum Toxin as a Biological Weapon – Medical and Public Health Management”, 2001, http://www.bt.cdc.gov/agent/botulism/botulismconsensus.pdf
[13] Nigam, PK and Nigam, Anjana, “BOTULINUM TOXIN”, Indian J Dermatol. 2010 Jan-Mar; 55(1): 8–14.
[14] Hanson, Doug Phd. “Botulinum Toxin: A Bioterrorism Weapon”, April 1st, 2004, http://www.emsworld.com/article/10324792/botulinum-toxin-a-bioterrorism-weapon
[15] Hanson, Doug Phd. “Botulinum Toxin: A Bioterrorism Weapon”, April 1st, 2004, http://www.emsworld.com/article/10324792/botulinum-toxin-a-bioterrorism-weapon
[16] Hanson, Doug Phd. “Botulinum Toxin: A Bioterrorism Weapon”, April 1st, 2004, http://www.emsworld.com/article/10324792/botulinum-toxin-a-bioterrorism-weapon
Chetan Hebbale 