Toxins may be countered by specific antisera and selected pharmacologic agents. It may be considered useful to classify biological agents by the effects they produce in an operational context, in order to provide guidance to the field commander on the consequences for continued operational effectiveness. Annex C of this manual provides guidance for such a classification scheme by individual agent. Operational categories should incorporate all recognized variables likely to impact on effectiveness, to include lethality, transmissibility, and persistence. Dissemination is the process by which infectious diseases or toxins are dispersed to cause disease or intoxication.
Biological agents are most likely to be delivered covertly and by aerosol.
Other routes of entry are thought to be less important than inhalation but are nonetheless potentially significant. The natural process of breathing causes a continuing influx of biological agent to exposed individuals. The major risk is pulmonary retention of inhaled particles. Still smaller droplets are inhaled, but they are not efficiently retained in humans. Smaller sized particles are not efficiently retained by the human respiratory tract and are relatively unstable under ambient environmental conditions.