A bioterrorism attack is the intentional release of a virus, bacteria, or biotoxin used to cause illness or death in people, animals, or plants.
An attack against the population could be used to cause illness, death, fear, socioeconomic disruptions.
An attack on animals and plants could be used to attack the food chain, cause, an economic disaster, and inflict illness and possibly death to humans.
There are two broad categories a biological agents. The first type are transmittable agents that spread from person-to-person such as smallpox. The second type of agent can cause illness in the individuals that are exposed to the aging itself but is not transmittable, for example anthrax.