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BIOBOMBS: THE CHAOS OF DISEASE

Though the unpredictability of biological weapons may be less important to terrorists than to war strategists, it may still be a major drawback. Even terrorists need a ballpark estimate of the damage they are likely to cause, and the sources of unpredictability are myriad. When terrorists use weapons, they are looking for a psychological effect, and such effects are likely to vary tremendously depending on the amount of damage inflicted. If a microbial attack fizzles, then the terrorist group would look like incompetent bunglers. If it got out of hand, killing, say, a million people instead of a thousand, then the reaction against the terrorist group might be so strong and unified that the terrorist act would be suicidal for the organization.The scope of damage is particularly difficult to estimate for biological weapons because the rate at which infections spread can increase geometrically. If one infected individual infects ten others, and each of those infects ten others, then a hundred infections will result after two rounds of transmission, a thousand after three rounds, and so on. If such an attack was recognized early enough to curtail the outbreak by only three cycles, the overall number of infected people could be reduced about a thousandfold. Conversely, if people were particularly slow to recognize what was happening, the outbreak could be several orders of magnitude greater. A terrorist therefore has a great chance of causing too little or too much damage depending on whether the outbreak is recognized a few hours earlier or later than planned.Dosage presents another source of unpredictability. Depending on the dosage, the net effect of microbial pathogens in most infections can vary from an infection without any symptoms to lethality. If most people get low dosages, the net effect of an attack might involve something more akin to vaccination than to a lethal epidemic. Those people who get high dosages and who are particularly vulnerable will tend to have very short incubation times. Variation in incubation times contributes to the uncertainty of the effect of a microbial attack by generating a large potential variation in the time of recognition of an outbreak.Dosage depends on all sorts of variables that are out of the control of the perpetrator, variables such as humidity, light intensity, and temperature. Most scenarios for the use of infectious weapons involve respiratory tract pathogens, which tend to be very sensitive to ultraviolet radiation. This sensitivity has several important consequences. It means that transmission of infection and effective dosages will be reduced if weather raises the intensity of ultraviolet light, or if weather causes people to stay outside rather than inside. It also means that the degree of within-building transmission relative to between-building transmission will depend on weather. The transmission dynamics of these two types of spread are bound to be different.Even if terrorists could master all the available knowledge from epidemiology and microbiology, tremendous uncertainty would still be associated with the effects of their actions. The best minds in these areas of science are nowhere close to being able to predict such details with accuracy. Unless terrorists can outclass the best minds in epidemiology, we can safely assume that the use of biological weapons would be a bad move by any terrorist looking to cause a particular severity of infectious outbreak.If attackers underestimated the scope of the outbreak, they would be likely to cause damage to unintended targets. Infectious agents do not restrict themselves to ethnic or national boundaries. Considering the uncertainties, we can expect consequences that may vary by several orders of magnitude. Predictive errors of much smaller magnitudes could subsume not only the targets of the attack but the attackers’ beneficiaries and allies as well, an extreme case of death by friendly fire. Such unintended targets may be in New York City one morning and at any other airport in the world the next day, spreading infection to other unintended targets.Terrorists could try to vaccinate those whom they wish to protect, but germs evolve. A germ generated during an outbreak might change its makeup, especially if it was a laboratory variant. A terrorist cannot tell whether a microbe will rapidly evolve changes in virulence or transmissibility, nor whether a vaccine that was protective against the germ that went into a target population will work against the germ that comes out.The terrorist needs sudden and spectacular devastation. Use of infectious agents compromises this goal because the devastation they can impose is constrained by a trade-off: high transmissibility is generally coupled to reduced lethality. If a pathogen is rapidly lethal, then it is generally not very transmissible. Terrorists attempting to cause a highly lethal outbreak will tend to have a short-lived outbreak. But if an infectious weapon is nontransmissible, it loses much of its fearful aspect, which arises from the prospects of a limited release spreading to engulf a large population. If transmissibility is maintained, virulence is reduced. The smallpox virus—probably the most dangerous transmissible infectious weapon—offers an illustration. The virus can be expected to kill about 20 percent of those who are infected. Although the number of deaths caused by the use of this agent would be horrific, it is important to realize that in the wake of a smallpox battle four out of five victims would survive. If a bomb killed only one out of five of the targets, the terrorist action would be considered a failure. More important for the terrorists, the survivors would be angry. The victims would be ready to take revenge on those responsible for killing their family and friends, and world opinion would be on their side. Draconian measures to root out the responsible terrorists would be all the more likely to be considered justified.*53\225\2*

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