Smallpox as a Weapon

Category A Agent

Variola virus is classified by the Center for Disease Control and Prevention as a Category A bioterrorism agent. Most agents in category A can cause infection by aerosol transmission, affect highly susceptible civilian populations, have a high morbidity and mortality, and are difficult to diagnose and/or treat. Some are transmitted from person to person. Smallpox has all of these characteristics. (19:4)

A comprehensive review of the problems posed by biological terrorism and warfare has been published. Four observations deserve special note. (7:2) Biological terrorism is more likely than ever before and far more threatening than either explosives or chemicals. Official actions directed at the threat to the civilian population have been only marginally funded and minimally supported. Preventing or countering bioterrorism will be extremely difficult. Recipes for making biological weapons are now available on the Internet, and even groups with modest finances and basic training in biology and engineering could develop, should they wish, an effective weapon at little cost. Detection or interdiction of those intending to use biological weapons is next to impossible. Looking at the ease of production, infection rates, and deadliness, both anthrax and smallpox seem the most likely weapons of choice for a serious assailant. (6:23)

Smallpox represents a serious threat to civilian populations because of its case-fatality rate of 30% or more among unvaccinated persons and the absence of specific therapy. (9:1) An aerosol release of variola virus would disseminate widely, given the considerable stability of the orthopoxviruses in aerosol form and the likelihood that the infectious dose is very small. Moreover, during the 1960s and 1970s in Europe, when smallpox was imported during the December to April period of high transmission, as many as 10 to 20 second-generation cases were often infected from a single case. (9:3)

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