Bioterrorism is the intentional release of biological agents to cause illness or death in humans, animals, or plants. These agents may be bacteria, fungi, toxins, or viruses. They may be naturally occurring or human-modified.
The agents are typically found in nature, but they may be altered in a laboratory to increase their resistance to antibiotics, and ability to spread in the environment. Biological and chemical agents may be spread through the air, food, or water. Terrorists use biological agents because they are often difficult to detect and illness onset may be delayed for hours to days increasing dispersal.