These disease agents differ from one another in several characteristics:

Clostridium botulinum, the
bacterium that causes
botulism

• Infectious Dose: The dose required to infect a human being ranges from as few as one to ten organisms for Q fever, to 100-500 organisms for the inhalational form of anthrax.


• Incubation Period: The delay between infection and the appearance of symptoms can range from as little as one day (for plague) to as many as 42 days (for anthrax).

Vibrio cholerae, the
bacterium that causes
cholera

• Duration and Mortality: The nature and seriousness of the illness resulting from infection may vary substantially. For example, Q fever is incapacitating but rarely fatal, whereas plague is nearly always fatal unless treated within 12 to 24 hours.



The Ebola virus

• Persistence in the Environment: The most effective way to disseminate a biological agent is in the form of an aerosol: a superfine mist of microscopic particles, similar to an invisible smoke, that would infect people by being inhaled into the lungs. Microbial agents can survive for varying amounts of time when dispersed as an aerosol. Most bacteria and viruses die rapidly after being released into the air, particularly when exposed to sunlight, but a few microbial agents are more robust. Anthrax bacteria, for example, can be induced to form tough, seed-like spores that will survive for several hours when released as an aerosol. The fall 2001 letter attacks also demonstrated that anthrax spores can contaminate the interior of buildings for years, requiring sterilization with costly techniques such as fumigation with a toxic gas.
• Contagiousness: Contagious diseases, such as smallpox and plague, can spread rapidly through a population by means of person-to-person transmission. In contrast, non-contagious agents, such as anthrax, infect only those individuals who are directly exposed and do not spread to others. For this reason, a bioterrorist attack with a non-contagious agent would be self-limiting, whereas an attack with a contagious agent could trigger an uncontrolled epidemic.


Lymph node from deceased
victim of anthrax

• Availability of Vaccines or Medical Treatment: Bacterial agents, such as those that cause anthrax, tularemia, and plague, generally respond to antibiotic drugs if they are given early enough after infection. In contrast, most viral diseases lack effective drug therapies, so that prevention through vaccination is the only option. In most instances, vaccination several months prior to exposure is required for effective protection, though in some cases post-exposure vaccination can boost immunity. Vaccines also vary in effectiveness and speed of action. For example, the smallpox vaccine induces protective levels of immunity within a few days after exposure. The anthrax vaccine, in contrast, requires multiple injections over a period of several months. Anthrax vaccine can be administered after exposure, but it must be used in conjunction with antibiotics for treatment of the disease. Bioterrorists may also consider the use of "non-traditional" disease agents that have not been developed as weapons by states. For example, certain types of Salmonella and E. coli bacteria can cause severe diarrhea that is incapacitating but usually not fatal. As noted in Chapter 2, in 1984, followers of the Baghwan Shree Rajneesh grew cultures of a strain of Salmonella bacterium that causes food poisoning and used them to contaminate restaurant salad bars in a nearby town.