Introduction

Biological agents are organisms or toxins that can cause deadly diseases in people, livestock and crops. The agents kill by spreading a disease that is normally fatal or by tricking the body's cells into producing a toxin that overwhelms its defenses. Only a small number of the hundreds of bacteria and viruses are viable as terrorist weapons because most cannot survive outside narrow temperature ranges or are too rare and hard to grow. There are different types of biological agents, including bacteria, viruses and toxins.

Biological agents can be handled easily and can cause great harm in small amounts. Drying the germs for use in a delivery system, such as an aerosol, is the most difficult part. The diminutive size of biological agents, five microns or less than one-fifth the width of human hair, means they can remain airborne for hours or, in still, dry weather, a day or more. Once inhaled, their size enables them to bypass the filtering mechanism in the upper respiratory system and enter the lungs and the bloodstream. It usually takes several days or weeks before the effects of biological agents become obvious.

Because biological agents cannot necessarily be detected and may take time to grow and cause a disease, it is almost impossible to know when an attack has occurred. The delayed onset of symptoms also creates potential for wider dissemination of the agent by infected people. If government officials become aware of a biological attack, they would most likely instruct residents to either seek shelter where they are and seal the premises or evacuate immediately.

In this section, we discuss anthrax, smallpox, botulism, plague and tularemia