A biological attack is the intentional release of a pathogen (diseasecausing agent) or biotoxin (poisonous substance produced by a living organism) against humans, plants, or animals. An attack against people could be used to cause illness, death, fear, societal disruption, and economic damage. An attack on agricultural plants and animals would primarily cause economic damage, loss of confidence in the food supply, and possible loss of life. It is useful to distinguish between two kinds of biological agents:
- Transmissible agents that spread from person to person (e.g., smallpox, Ebola) or animal to animal (e.g., foot and mouth disease).
- Agents that may cause adverse effects in exposed individuals but that do not make those individuals contagious to others (e.g., anthrax, botulinum toxin).
Availability of Agents
The Centers for Disease Control and Prevention (CDC) lists the biothreat agents considered to pose the highest threat. Once obtained, agents must be cultured or grown in quantity and then processed for use in an attack ("weaponized"). Agents can be:
- Isolated from sources in nature. These threat agents are either biotoxins or agents that cause zoonotic diseases (that occur in wildlife and are transmissible to humans)—except for smallpox, which is solely a human disease and has been eradicated from nature.
- Acquired from laboratories or bioweapons stockpile. Smallpox virus is officially studied in only two laboratories in the world. Anthrax is widely studied in labs. Hemorrhagic fever viruses are studied only in limited high-security locations. Most high threat agents had been studied and stockpiled in bioweapons programs outside the United States until as recently as the 1990s.
- Synthesized or genetically manipulated in a laboratory. This would require expertise and access to advanced technology.
How Biological Agents Could Be Disseminated
For an attack on people, biological agents could be disseminated in one or more of the following ways:
- Aerosol dissemination is the dispersal of an agent in air from sprayers or other devices. The agent must be cultured and processed to the proper size to maximize human infections, while maintaining its stability and pathogenicity (ability to produce illness). An aerosol attack might take place outdoors in a populated area or indoors, e.g., in the ventilation system of a building, in the subway, on planes. It takes expertise to process biological agents to maximize the effect of aerosol dissemination, but even relatively crude devices could have an impact.
- Food or water, especially ready-to-eat food (vegetables, salad bars) could be intentionally contaminated with pathogens or toxins. The water supply is less vulnerable because dilution, filtration, and the addition of chlorine can kill most disease-causing organisms.
- Human carriers could spread transmissible agents by coughing, through body fluids, or by contaminating surfaces. Most agents would make people ill or incapacitated before they become highly contagious, thereby reducing transmission of the disease.
- Infected animals can cause people to become ill through contact with the animals or contaminated animal products.
- Insects naturally spread some agents such as plague bacteria (vector-borne illnesses) and potentially could be used in an attack.
- Physically distributed through the U.S. mail or other means.
For an agricultural attack:
- A point introduction of an infected plant or animal or its fluids could spread disease through the rest of the crop or livestock. Agricultural biothreat agents (e.g., foot and mouth disease, avian influenza, soy bean rust, and karnal bunt of wheat) do not have to be aerosolized to be effectively disseminated.
Impact Following the Release of a Pathogen
Detection of a Biological Attack
Unlike a chemical or nuclear attack, a biological attack may go undetected for hours, days, or potentially weeks (depending on the agent) until people, animals, or plants show symptoms of disease. If there are no immediate signs of the attack as with the anthrax letters, a biological attack will probably first be detected by local health care workers observing a pattern of unusual illness or by early warning monitoring systems that detect airborne pathogens. Evidence of an attack may appear in animals before humans.
The Area Affected
For an aerosol release, the area affected would depend on the quantity of agent released, whether the release is indoors or outdoors, and weather conditions. Agents released outdoors would disperse roughly in the direction of the prevailing wind and could degrade with sunlight and by drying out from environmental exposure. Agents released indoors could initially have a higher concentration. Sometimes agents can be re-aerosolized by machinery, foot traffic, or other means.
Finding the Cause and Source of Illness
There may be uncertainties about crucial facts such as the exact location or extent of the initial release, the type of biological agent used, and likelihood of additional releases. Laboratory scientists will work quickly to identify the specific agent. Epidemiologists will attempt to trace the path of infections back toward a single person, vector (insect or animal), vehicle (food or water), or other point of origin. Attribution of a biological attack is typically much more difficult than attribution of a conventional terrorist attack.