 |
|
Categorizing Agents of Bioterrorism Concern
 he
U.S. Centers for Disease Control and Prevention (CDC)
has categorized
potential bioterrorism agents according to level of threat, using the
following criteria:
- Public health impact, such as transmissibility
and ability to cause illness and death;
- Ease of production;
- Ability to cause grotesque or frightening symptoms that induce terror;
- Requirement for special preparations to "weaponize" (make usable as a weapon) or
disseminate the agent;
- Potential for delivery as an aerosol or by contamination of food or water.
On this basis, the CDC has classified
potential bioterrorism threat agents into three categories, designated
A, B, and C. Category A, which poses the greatest threat, includes the
disease agents of smallpox, anthrax, plague, botulism, tularemia, and
viral hemorrhagic fevers.
Smallpox, which is classified as a Category A
agent, was eradicated as a natural disease in 1977 through a global
vaccination campaign run by the World Health Organization (WHO). The
last case of the disease resulted from a laboratory accident in Birmingham,
England in 1978. Since the mid-1980s, all official stocks of the smallpox
virus have been restricted to two WHO-approved repositories in the United
States and Russia, currently at the CDC in Atlanta, Georgia, and the
"Vector" laboratory in Koltsovo, Siberia.
Day 4 rash after exposure to smallpox virus (Source: CDC website)
Nevertheless, circumstantial
evidence suggests that undeclared stocks of the smallpox virus may exist
in Russia, North Korea, and perhaps other countries. Also worrisome
is the fact that during the Cold War, the Soviet Union developed
the smallpox virus as a biological weapon for use against U.S. and Chinese
cities in the event of World War III.
If employed as a terrorist weapon, smallpox would have a severe public
health impact because:
- It is highly transmissible from person to person
(although not as
contagious as influenza or measles);
- The psychological impact of the disease is great because it produces
a painful and disfiguring rash that leaves survivors permanently scarred;
- The virus is highly virulent (capable of causing disease), with the most
lethal strains causing 30 to 40 percent mortality;
- At least 80 percent
of the U.S. population is susceptible to smallpox infection. The United
States stopped mandatory vaccination of children in 1972, and all individuals
born since then (excepting those who have served in the military and
some health workers) have
not been vaccinated. Evidence also suggests that the protective immunity
provided by the vaccine wanes over time, so that adults who were vaccinated
as children are probably not fully protected today.
Public health specialists
at Johns Hopkins University have argued that if even a single case of
smallpox was diagnosed in the United States, it might be necessary to
shut down the entire U.S. air transport system for as long as a month
to prevent infected individuals from spreading the disease nationwide.
The severe economic consequences of such a step suggest the potential
devastating "domino effect" of even a small-scale bioterrorist attack
with a contagious agent. Even so, it is important not to exaggerate
the threat of smallpox. The virus would be extremely difficult for terrorists
to obtain because it no longer exists in nature.
See detailed analysis of all these biological
agents in the Biological Agent Primer of the multimedia section.
|
|
|