Toxins are defined as any toxic substance of natural origin produced by an animal, plant, or microbe. They are different from chemical agents such as VX, cyanide, or mustard in that they are not man-made. They are non-volatile, are usually not dermally active (mycotoxins are an exception), and tend to be more toxic per weight than many chemical agents. Their lack of volatility also distinguishes them from many of the chemical threat agents, and is very important in that they would not be either a persistent battlefield threat or be likely to produce secondary or person to person exposures. Many of the toxins, such as low molecular weight toxins and some peptides, are quite stable, as where the stability of the larger protein bacterial toxins is more variable. The bacterial toxins, such as botulinum toxins or shiga toxin, tend to be the most toxic in terms of dose required for lethality (Appendix C), whereas the mycotoxins tend to be among the least toxic compounds, thousands of times less toxic than the botulinum toxins. Some toxins are more toxic by the aerosol route than when delivered orally or parenterally (ricin, saxitoxin, and T2 mycotoxins are examples), whereas botulinum toxins have lower toxicity when delivered by the aerosol route than when ingested. However, botulinum is so toxic inherently that this characteristic does not limit its potential as a biological warfare agent. The utility of many toxins as military weapons is potentially limited by their inherent low toxicity (too much toxin would be required), or by the fact that some, such as saxitoxin, can only feasibly be produced in minute quantities. The relationship between aerosol toxicity and the quantity of toxin required to provide an effective open-air exposure is shown in Appendix D. The lower the lethal dose for fifty percent of those exposed (LD50), in micrograms per kilogram, the less agent would be required to cover a large battlefield sized area. The converse is also true, and means that for some agents such as ricin, very large quantities (tons) would be needed for an effective open-air attack.
Where toxins are concerned, incapacitation as well as lethality must be considered. Several toxins cause significant illness at levels much lower than the level required for lethality, and are thus militarily significant in their ability to incapacitate soldiers.
This manual will cover four toxins considered to be among the most likely toxins which could be used against U.S. forces: botulinum toxins, staphylococcal enterotoxin B (SEB), ricin, and T-2 mycotoxins.
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