Chemical terrorism: The role of the large animal veterinarian (Proceedings)

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Chemical terrorism: The role of the large animal veterinarian (Proceedings)

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Aug 01, 2008

Currently, it is hard to avoid being made aware of biological, radiological and chemical threats to the U.S. and efforts to prevent and manage such threats. In veterinary medicine, there has been much discussion about new and emerging diseases caused by infectious agents such as the West Nile virus and the BSE prion and the vulnerability of U.S. agriculture to introduced diseases such as foot-and-mouth disease. Indeed, a number of reports point out how easy it would be for terrorists to target our agricultural and food industries and cause significant economic damage. Unfortunately, agroterrorism discussions have largely focused on infectious threats, with much less attention paid to chemical and radiological threats. The purpose of this talk is to illustrate how chemicals and "dirty" bombs might impact animal agriculture. It is important to point out that a small quantity of environmentally persistent chemicals such as dioxin and polychlorinated biphenyls (PCBs) are capable of causing major disruptions to one or more animal agricultural sectors. The recent pet food recall due to contamination of imported commodities with melamine and cyanuric acid demonstrate the vulnerability of our food supply.

In my view, there are three potential scenarios in which chemicals or radiological agents could be utilized in an agroterrorist context. The first scenario would involve the use of an agent on a small scale to test potency, delivery methods or laboratory diagnostic capabilities. In the latter situation, it might be important to know whether the introduction of a chemical agent is quickly identified and contained or not. Agents that are not readily identified are more likely to have widespread distribution than agents that are detected easily. In such scenarios, there is the possibility of limited animal death losses.

The second scenario would be an attempt to kill a large number of animals. With the increasing concentration of animals in the U.S., it would not be hard to imagine death losses in the thousands. Although it would be conceivable to kill large numbers of confined animals with a gaseous agent such as cyanide, it would be much easier to cause mortality by way of the feed. There are a number of highly toxic, readily obtainable chemical agents, such as organophosphate or carbamate insecticides that could be used for such purposes. While the economic impact nationally from the deaths of even thousands of animals would be relatively small, the emotional impact could be great.

The third scenario involves the widespread contamination of animal feed and animal products with persistent, but not necessarily acutely toxic, chemicals. The use of such agents would be designed to cause significant economic disruption by rendering animal products unsuitable for human consumption. The idea would be to cause residues in animal products such as meat, milk and eggs sufficiently high that the products would be considered adulterated and potentially damaging to human health. Such residues could be achieved without necessarily causing significant animal illness or mortality. This latter fact makes such a scenario appealing from the standpoint that widespread contamination could occur prior to recognition of the problem. Good examples of agents that could be used include dioxins, such as TCDD, PCBs, and organic mercury compounds. Additionally, substantial radiological contamination of animal products might occur prior to detection of abnormal radioactivity.

There are several characteristics of chemicals that are considered "ideal" when thinking about their use against people. Agents should be toxic at low doses and quickly incapacitating. In addition, there should be no effective antidote available. The agent should be easily handled and able to be aerosolized or vaporized to maximize exposure via inhalation or dermal exposure. The agent should be readily available or easily made and relatively cheap. There are a number of "classic" chemical agents that have been used including nerve agents (organophosphates such as sarin, soman, and VX), blister agents such as mustard gases, choking agents such as phosgene, so called "blood" agents such as cyanide and relatively recently discussed agents such as ricin and botulinum toxin. All fit the definition of an "ideal" agent to a greater or lesser degree. Many of these agents could be utilized in the 2nd scenario as outlined above.

Ideal characteristics of agents for use in the 3rd scenario are substantially different than those listed above. The agent should be relatively non-toxic acutely to avoid significant animal death losses soon after exposure. The agent should be highly lipophilic, thus ensuring persistence in the animal or animal product. There should be no practical way to decontaminate exposed animals. There should be public health concerns about exposure to low concentrations of the agent. Finally, similar to the agents given above, the agent should be easily produced or available, easily handled and relatively cheap. Chemicals that fit the above criteria include dioxins, PCBs, and organic forms of mercury.