Anthrax has been designated as the number one biological warfare threat to the U.S. military and the American homeland. It is likely to be the weapon of choice based on its weaponization potential, ease of production, ease of delivery as aerosolized spores, and the lethality of the inhalational form of the disease.
The Department of Health and Human Services has adopted a scenario planning model based on research conducted at Stanford University. The model illustrates what would occur in a large-scale anthrax attack. It has been determined that a one kilogram release of anthrax spores would affect an urban area of over 30 kilometers, exposing 11.5 million people to anthrax and infecting 1.5 million people. Of those infected, more than 120,000 would be expected to die. In addition, the economic impact of such an attack would be tremendous. The total economic impact of the 15 grams of anthrax used in the 2001 anthrax attacks has been estimated at more than $6 billion.
Anthrax is particularly virulent due to its ability to evade and impair the immune system. Once inhaled, spores less than 5 mm can become deposited in the lung’s alveoli where they are ingested by macrophages and transported to mediastinal lymph nodes. These spores then germinate into viable bacteria, typically causing a hemorrhagic mediastinitis and subsequent bacteremia. A poly-D-glutamic acid capsule inhibits phagocytosis of the bacterium, while two toxins (lethal toxin and edema toxin) further impair the immune system by killing macrophages and inhibiting phagocytosis. With an impaired immune system, bacteria replicate freely and toxin production results in hemorrhage, edema, and necrosis.