pose high-level risks. Security guards, surveillance systems, personnel checks, and testing of personnel can be used to ensure that such biological agents are not removed from research facilities.

In contrast, biological agents with the potential to damage U.S. agriculture most often occur naturally in some part of the world. These agents can easily be obtained (domestically or overseas) and can readily be released, given the general lack of security on farms and fields and their formidable size. For example, foot-and-mouth disease was widespread in the United Kingdom in 2001. A shoe from someone who walked on an infected farm would have been able to carry enough of the agent into the United States to cause an outbreak. Although U.S. border inspections for such potential introductions were heightened during the outbreak in the United Kingdom, the methods used were heavily dependent on the honest answers and voluntary compliance of the traveling public. It is likely that a determined terrorist could circumvent such an interdiction approach.

Similar issues arise for plant pathogens and pests. For example, citrus canker is a bacterial disease of woody perennials that is endemic in several parts of the world where citrus is grown. It has recently been reintroduced into the United States, in Florida, and has had significant adverse impacts on the state’s citrus industry. For agriculture, given that would-be terrorists have access to various naturally occurring threats, it will also be important to consider the possibility of the intentional release of multiple types of agents at multiple sites.

For biological agents that may be used by terrorists and that occur naturally, it is appropriate to use lower levels of security and less direct oversight. The level of such oversight may still be significant and should be designed to offer real protection against the acquisition of biological agents that may be used as weapons. Significantly higher levels of security should be applied to any weaponized biological agents—for example, anthrax spores that have been treated to make them easily aerosolized.

The diversity of existing biological weapons and the ever-increasing number of possibilities through use of genetic recombination preclude simple therapeutic countermeasures to bioterrorism. The Soviets are known to have developed at least 30 biological agents. While it might only take 1 to 3 years to develop a new biological weapon, the average development time of a new drug or vaccine is 8 to 10 years. Thus with respect to development of countermeasures for biological weapons, a great need exists for broad-spectrum antibiotics and antivirals. Based on current knowledge, technology, and genomic databases, the goal of broad-spectrum anti-infectives is achievable.

Existing countermeasures for known threats are limited. For the potential biological weapons on the CDC “A” list, there are only two vaccines available or in production (anthrax and smallpox), one antiviral, and a limited number of