Many bacteria, fungi, viruses, rickettsial agents, and toxins have been mentioned in various literature sources as possible biological warfare agents. Those mentioned most often include Bacillus anthracis (anthrax), botulinum toxin, Yersinia pestis (plague), ricin, Staphylococcal enterotoxin B (SEB), and Venezuelan equine encephalitis virus (VEE). Despite the very different characteristics of these organisms, viruses, and toxins, biological agents used as weapons share some common characteristics. They can be dispersed in aerosols of particle size one to five micrometers (microns), which may remain suspended (in certain weather conditions) for hours and if inhaled will penetrate into distal bronchioles and terminal alveoli of victims. Particles larger than five microns would tend to be filtered out in the upper airway. The aerosols may be delivered by simple technology, including industrial sprayers with nozzles modified to generate the smaller particle size. The aerosol could be delivered from a line source such as an airplane or boat traveling upwind of the intended target, or from a point source such as a stationary sprayer or missile dispensing agent-containing bomblets in an area upwind of the target. The weather in the target area is very important in the employment of biological agents as aerosols, as higher wind speeds tend to break up the aerosol cloud, and stable wind direction is obviously important. Inversion conditions and lower wind speeds, 5 to 10 miles per hour, conditions which occur more often during nighttime and early morning hours, would be ideal for dispensing such aerosols. Other possible routes of exposure for biological agents include oral, by intentional contamination of food and water, and percutaneous. In general, these other routes of exposure are considered less important than the respiratory route.

Diseases produced by the offensive use of biological agents against U.S. forces could be lethal and/or disabling. From a military standpoint, incapacitation of a high percentage of friendly forces may be as operationally significant as effects caused by more lethal agents. Examples of lethal agents include Bacillus anthracis, botulinum toxin, and Francisella tularensis, while incapacitating agents include SEB and Coxiella burnetii. Some agents, such as Yersinia pestis and C. burnetii, would produce pulmonary syndromes characteristic of the endemic disease they produce in nature. Others, such as botulinum toxin, although delivered by a different route of exposure (respiratory) than usual with endemic disease, would produce a similar clinical picture to that commonly seen with oral exposure. Person-to-person spread could be important for some agents, such as smallpox and pneumonic plague, and local disease cycles might occur if a competent vector for a bacterium or virus is present in the environment (e.g., fleas for Y. pestis and certain mosquitoes for Venezuelan equine encephalitis).

The potential impact of biological weapons is well illustrated by a World Health Organization publication from 1970 (Health Aspects of Chemical and Biological Weapons, WHO, 1970). It was estimated that fifty kilograms of aerosolized B. anthracis spores, for example, dispensed by a line source 2 kilometers upwind of a population center of 500,000 unprotected people in ideal meteorological conditions, would travel greater than 20 kilometers downwind, and kill/incapacitate up to 125,000 people in the path of the biological cloud. If F. tularensis was dispensed, the number of dead/incapacitated was estimated to be about 125,000. Thus, if properly employed as offensive weapons under ideal meteorological conditions, certain biological organisms could truly be weapons of mass destruction.

In addition to their detrimental health effects on the targeted population, biological warfare agents would likely cause significant impacts on the medical care system. Overwhelming numbers of patients, and demands for intensive care would overwhelm medical resources. Special medications or vaccines not generally available in standard pharmaceutical stocks would be required. Medical care providers and laboratory personnel might need added protection, and autopsy and interment of remains could present hazards not commonly dealt with.

The medical response to the threat or use of biological weapons may be different depending on whether medical measures are employed prior to exposure, or whether exposure has already occurred and/or symptoms are present. If provided before exposure, active immunization or prophylaxis with antibiotics may prevent illness in those exposed. Active immunization may be effective against several potential biological warfare agents, and is probably the best modality for future protection of U.S. military forces against a wide variety of biological threats. After exposure, active or passive immunization as well as pre-treatment with therapeutic antibiotics or antiviral drugs may ameliorate disease symptoms. After onset of illness, only diagnosis of the disease and general or specific treatment are left to medical care providers. The good news is that excellent vaccines and antitoxins exist for several of the most likely biological warfare agents, and more are under development.