Biological attacks involve bacteria, viruses, or natural toxins. The effects of toxins can be immediate but for bacteria and viruses the effects may not be apparent for weeks. A bioterrorist may attack by infecting animals, contaminating food and water, spraying bacteria or viruses into the air. In infections such as smallpox and plague, once a few individuals are infected they can further spread the disease from person to person. An attack could also come through a building's ventilation system, the mail, or even through exposure to an infected terrorist seeking to spread disease during an infectious stage.
