enough is known that we can begin to predict where second-generation vaccines and various antitoxin modalities might work.
Unlike anthrax, smallpox is a contagious disease with fairly high rates of human-to-human transmission. Consequently, smallpox is considered to pose an even greater threat as an agent of biological terrorism than anthrax (Henderson et al., 1999). Smallpox represents a threat whose consequences are potentially catastrophic; hence it requires careful attention, regardless of the probability of its use. Several features make it an attractive bioterrorist agent: it is moderately stable; it is infectious by droplets and aerosol; it is moderately contagious; and, because vaccination against smallpox ceased after eradication in 1980, most of the world’s population is highly susceptible to infection.
While a smallpox vaccine exists, several bioterrorism-related issues regarding prophylactic smallpox vaccination are unresolved (IOM, 2003). Therefore, we must develop clinician awareness, diagnostic systems, and stockpiles of existing vaccine that will give us a validated countermeasure to deploy in case of the intentional use of this biological agent.
Yersinia pestis poses a risk to national security because this pathogen can be disseminated by aerosol and/or transmitted from person-to-person, could cause high mortality, and requires special action for public health preparedness (CDC, 2000b). Plague was weaponized in the former Soviet Union for aerosol delivery, and engineered for antimicrobial resistance and possibly enhanced virulence (Inglesby et al., 2000). Plague cultivation in virulent form and its dissemination in stable aerosols, however, are more difficult than is the case for anthrax. Plague generates special concern because of its potential to cause panic, its contagiousness in the pulmonary form, its fulminating clinical course and high fatality, and the possibility that it could be engineered for plasmid-mediated resistance to multiple antimicrobial agents (Galimand et al., 1997). In the WHO modeling scenario that was developed in 1970, a 50 kg release over a city of 5 million would cause about 150,000 cases and 36,000 deaths in the first wave (WHO, 1970). A secondary spread would cause a further 500,000 cases and 100,000 deaths. Plague requires intensive medical and nursing support and isolation for at least the first 48 hours of antibiotic treatment, followed by 2 to 3 weeks of slow convalescence. The hospitalization and isolation that would be required for this number of people in a single city is nearly unimaginable. Pneumonic plague’s contagiousness would require isolation