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In order to be effective as a weapon, an agent needs to be highly infective, be stable enough to resist degradation during handling and storage, and be spread in a such way that the necessary infective dosage is delivered to the target population.

Biological agents may be bacteria, rickettsiae, chlamydia, viruses or toxins. While thousands of pathogenic microorganisms have been investigated for their potential utility as weapons, only some forty biological agents have been identified as satisfactory candidates, for examples, Bacillus anthracis (anthrax), Yersinia pestis (plague), Variola major (smallpox), Brucella species (brucellosis) and Salmonella typhi (typhoid fever).

Biological agents can be characterized by their intrinsic features, notably infectivity, virulence, lethality, pathogenicity, incubation period, mode of transmission and stability, all of which influence their potential for use as weapons.

The most immediate consequence of incidents involving biological weapons is their ability to cause mass casualties and their potential for overwhelming medical resources and infrastructure secondary to psychological reaction of the population to the attack. They may also have the potential for causing physical or mental illnesses months or years after the attack.

Public Health Preparedness and Response

The first indication of an incident could be a warning, or the finding of an unusual device or unusual materials. One or more of the following activities may be required :

• analysis of available information
• initiation of a search procedure for a suspect device or location
• establishment of a cordon
• hazard reduction and/or neutralization
• early identification of a nature of the hazard, whether it is biological, chemical or mixed

Generally speaking, a biological agent attack would have the characteristics of a disease outbreak. Establishing routine sensitive and near real time disease surveillance systems will serve a dual purpose in natural and deliberate outbreaks.

Response to an established biological attack is a multidisciplinary and complex task, which will require co-operation between civil defence, emergency response, law enforcement, public health and medical personnel. The requisite response activities can be identified through the principles of risk management.

1. Identify the hazards
   Identify the nature of agent involved; define the population at risk and develop an initial hypothesis on the source of the agent and mode of transmission.
   
   

2. Evaluate the hazards to determine initial risk
   Evaluate potential outbreak spread, and assess current and delayed case management requirements.
   
   

3. Introduce risk reduction strategies
   Implement a risk communication programme for the affected population that conveys information and instructions as needed; order necessary supplies and organize needed personnel; protect responders and healthcare workers; introduce infection prevention and control procedures and ensure medical care of infected cases.
   
   

4. Quantify the residual risk, and make a risk acceptance decision
   Decide whether local resources are adequate and whether international resources should be accessed.
   
   

5. Monitor the risk management programme, and repeat the process as
   required
   Implement active surveillance to monitor the effectiveness of prevention and control procedures and follow up activities.