Beyond the Usual Suspects: Biological Agents

In the wake of the 9/11 attacks, Americans were gripped by a fear that other attacks would soon follow. This fear also included the potential for an attack with a biological warfare agent. Then, in September and October of that year, a series of letters containing militarized anthrax spores was sent to various government and news agencies. Experts believed the anthrax was "militarized," or military-grade, material produced in a sophisticated laboratory, like a government facility, and not a "homegrown" variety that might come from a foreign terrorist group.

     Biological agents are considered the "poor mans' atomic bomb" because they can be produced relatively cheaply, with laboratory equipment that is easy to obtain and by technicians without a great deal of expertise. The phrase poor man's atomic bomb was originally used in 1988 before the Iranian Parliament by Speaker Hashemi Rafsanjani, who was comparing biological agents to nuclear weapons. It has since been echoed by U.S. news agencies and members of Congress.1

     Concern about attacks with biological agents usually centers around organisms like anthrax, smallpox, the Ebola virus or toxins like botulinum toxin-that is, the usual suspects. But there are many other organisms that could be used.

Beyond the Usual Suspects
     The Centers for Disease Control and Prevention has defined three levels of agents with potential as bioterrorist weapons: Categories A, B and C.2 Category A includes anthrax, smallpox, botulinum toxin and viruses, like Ebola, that cause viral hemorrhagic fevers (VHFs). It also contains plague (Yersinia pestis) and tularemia (Francisella tularensis).

     Category B includes a list of 47 agents containing bacteria that cause brucellosis (Brucella species), Q fever (Coxiella burnetii), typhus (Rickettsia bacteria, particularly Rickettsia prowazekii) and a variety of viral encephalitis diseases. Also in Category B are toxins like ricin (castor beans), epsilon toxin (Clostridium perfringens) and Staphylococcal enterotoxin B. The incubation time and symptoms for these agents are included in Table 1.

     The harm these agents can cause is impacted by a variety of factors, including environmental conditions like temperature, rain, humidity and wind. A full discussion of these environmental factors is beyond the scope of this article, but see reference No. 3 (Eitzen) for more details.

     Regardless of what agent is used in an attack, bioagents all share one characteristic that is not found in other weapons of mass destruction: incubation period, or the length of time between exposure and the start of symptoms.4 With biological agents, exposure does not necessarily mean infection. Infection depends on the dose of agent received, the host's natural immunological resistance and the overall health of the exposed individual.

     Individuals may be exposed to an agent at an indoor sporting event, large mall or other area. When leaving the area, they won't yet be contagious and won't immediately begin to spread the disease to others. Keep in mind, however, that exposed people can transfer some infectious agents to others through contact with their contaminated clothing, hair or items they might be carrying. The ability to infect others does not occur until after the incubation period; depending on the agent, this could take from several days to as long as three weeks. This lag can make it almost impossible to immediately determine that an attack has taken place. Only when multiple victims exhibiting similar signs and symptoms begin showing up at clinics and hospitals and activating EMS through 9-1-1 will a pattern suggesting common exposure begin to emerge. Medical investigators and law enforcement will have to develop a backward timeline to determine where infected individuals had been over the preceding days and weeks. Identifying a common location will help them deduce the place, date and time of the attack.