BioAgents and Epidemic Diseases Background Information

Categorization and Ongoing Assessment of Biological Agents
Anthrax, botulism, plague, smallpox, tularemia, and viral hemorrhagic fevers are diseases caused by the Category A biological agents, so-called because they pose particularly serious threats as bioweapons. The approach to prioritization and categorization of agents is now evolving. The Center’s experts inform and guide the risk assessment process and identify gaps in current preparedness efforts.

In 1999, the Working Group on Civilian Biodefense expert panel reached consensus on the following list of key features of biological agents that pose particularly serious risks if used as weapons against civilian populations:

• High morbidity and mortality
• Potential for person-to-person transmission
• Low infective dose and highly infectious by aerosol dissemination, with a commensurate ability to cause large outbreaks
• Effective vaccine unavailable or available only in limited supply
• Potential to cause public and healthcare worker anxiety
• Availability of pathogen or toxin
• Feasibility of large-scale production
• Environmental stability
• Prior research and development as a biological weapon.

The U.S. Centers for Disease Control & Prevention (CDC) applied the following 4 criteria to assess and characterize potential biological weapon agents that cause infections in humans into Categories A, B, and C:

1. Potential public health impact, which is based on an agent’s ability to cause illness and death
2. Dissemination potential, which is based on an agent’s stability, mass production and/or delivery potential, and the contagiousness, or the degree to which it will spread from person to person
3. Public perception, which is an estimation of how much fear is associated with an agent and how much civil disruption might ensue
4. Special public health preparations required, which is related to the stockpile, surveillance, and diagnostic requirements associated with an agent.

 
Ongoing Assessment of Biological Agents
The CDC’s Category A, B, and C agents do not constitute all of the agents that could potentially be used as biological weapons against humans. The Secretary of the Department of Homeland Security (DHS), in consultation with the Secretary of Health and Human Services (HHS) and the heads of other agencies, as appropriate, is required to assess on an ongoing basis the current and emerging threats posed by chemical, biological, radiological, and nuclear agents and determine which agents present a material threat against the United States sufficient to affect national security (42 USCS § 247d-6b). If DHS determines that a particular agent poses a material threat to the nation, it issues a Material Threat Determination (MTD) for that agent, which then initiates the BioShield process to procure countermeasures against that agent. To date DHS has issued MTDs for anthrax, botulinum toxin, smallpox, and radiological/nuclear threats. Additional MTDs are in process.

Beyond issuing MTDs to guide the BioShield countermeasure acquisition process, DHS is tasked with conducting periodic risk assessments of the evolving biological weapons threat in support of HSPD-10, Biodefense for the 21st Century. Under HSPD-10, DHS is to conduct a “formal process for conducting routine capabilities assessments to guide prioritization of our on-going investments in biodefense-related research, development, planning, and preparedness . . . [which] . . . identifies continuing gaps or vulnerabilities in our biodefense posture, and makes recommendations for re-balancing and refining investments . . . [in] . . . our overall biodefense policy.” DHS completed its first biological agent risk analysis on 28 biological agents of human concern on January 31, 2006, and produced a classified report on October 1, 2006. DHS is in the process of issuing MTDs for those agents that were found to pose a material threat to the United States in this assessment; however, the results have not yet been made public.

What to Expect in the Future
To date, the approach to assessing the biological weapons threat has focused on specific biological agents that have and/or can be employed as biological weapons. However, the threat space for biological weapons is larger than so-called ‘traditional agents’ and is growing as a result of continuing advances in biotechnology and emerging infectious diseases. In September 2006, in an effort to address the expanding threat from biological weapons, HHS published a “Draft HHS Public Health Emergency Medical Countermeasures Enterprise (PHEMCE) Strategy for Chemical, Biological, Radiological and Nuclear (CBRN) Threats.” In it, HHS recognized four types of threat agents:

• Traditional bioagents are “naturally occurring microorganisms or toxin products with the potential to be weaponized and disseminated to cause mass casualties.” [Federal Register. 2006; 71(174)].
• Enhanced agents are those that are modified to circumvent current countermeasures—for example, microorganisms that are purposefully manipulated to be resistant to multiple antibiotics, thus complicating a public health response in the aftermath of an attack.
• Emerging agents are those that occur naturally but are newly recognized or anticipated to pose a public health threat; e.g., a highly lethal and readily transmissible influenza strain that may cause a pandemic.
• Advanced agents are novel microorganisms that may be created by employing laboratory methods.

HHS expects to issue a final PHEMCE Strategy and an implementation plan for the strategy, and future threat assessments can be expected to move beyond traditional agents.