Terrorists could select from a long list of organisms to employ as bioweapons, but five biological agents cause the most concern. They are widely known and have the potential to pose the most serious threats to civilian populations.

An acute infectious disease caused by the spore-forming bacterium Bacillus anthracis.

Symptoms: Cutaneous anthrax: starts with a welt or swelling that progresses from a fluid-filled blister to a black, ulcerous lesion. Inhalation anthrax: resembles a common cold and develops into severe breathing problems and shock.

Time Frame: Symptoms usually occur within 7 days of exposure; sometimes as late as 6 to 8 weeks after exposure.

Infection: It does not transmit person to person. Anthrax infection follows contact with infected animals or contaminated animal products. Inhalation anthrax, the deadliest form, results from exposure to airborne spores. Cutaneous anthrax, caused by exposure of the skin to anthrax spores, is the most common form. Gastrointestinal anthrax also occurs, though rarely.

Fatality without Treatment: Inhalation anthrax is estimated to be 70 to 90 percent fatal. About 20 percent of cutaneous anthrax is fatal without


Botulism is a muscle-paralyzing disease caused by a toxin made by a bacterium called Clostridium botulinum.

Symptoms: Double vision, blurred vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth, and muscle weakness.

Time Frame: Symptoms begin within 2 hours to 8 days.

Infection: Botulinum toxin can spread through the air or food supply. It does not transmit person to person.

Fatality without Treatment: About 8 percent.

This highly contagious bacterium, Yersinia pestis, is found in rodents and fleas and can be easily grown and disseminated by aerosol.

Symptoms: Fever, headache, weakness, and cough productive of bloody or watery sputum.

Time Frame: Symptoms within 1 to 6 days of exposure. Without treatment, death occurs within 2 to 4 days after onset of symptoms.

Infection: Person-to-person transmission of pneumonic plague occurs through respiratory droplets, which can only infect those who have face-to-face contact with the ill patient. The most common infection occurs by plague-infected fleas biting humans, who then develop bubonic plague.

Fatality without Treatment: Nearly 100 percent.

Smallpox, caused by the Variola virus, is seen as one of the most serious bioterrorist threats because of its high case-fatality rates and transmissibility.

Symptoms: Fever, fatigue, headaches, and backaches followed by rashes and lesions.

Time Frame: First symptoms present 7 to 17 days after exposure. Death can occur within 2 weeks of symptoms.

Infection: Smallpox is spread from one person to another by infected saliva droplets that expose a susceptible person having face-to-face contact with the ill person.

Fatality without Treatment: About 30 percent.

Francisella tularenis, the organism that causes tularemia, is one of the most infectious pathogenic bacteria known — inhalation of as few as 10 organisms can cause disease.

Symptoms: Fever, fatigue, chills, swollen lymph nodes, and pneumonia.

Time Frame: Onset of symptoms begins in 1 to 14 days.

Infection: Human infection occurs through handling infectious animal tissues or fluids; direct contact or ingestion of contaminated water, food, or soil; and bites by infected insects, arachnids, or crustaceans.

Fatality without Treatment: 5 to 15 percent for severe Type A strains; 30 to 60 percent if infection in lung or bloodstream.

Note: See Fighting Bioterror for treatment and vaccine information.

Sources: CDC; Johns Hopkins Center for Civilian Biodefense Studies

By Brian Simpson
Photographs by John Dean

What does "weaponized anthrax" really mean?
DAH: [Laughs ruefully]. "Weaponization" was a term used in the military. One major criterion for putting an agent on [a defense] threat list was some evidence the organism had been weaponized… [put] in a bomb or a missile or a shell that would be a problem for the military forces. We had clear evidence from the very first case in Florida that there was anthrax produced in the dried form, which caused inhalation anthrax. And no one produces anthrax in that way for any other purpose than for causing disease and using this as a biological weapon.

In the public's mind, weaponized anthrax is a highly refined anthrax that's likely to cause inhalation anthrax.
DAH: That's right, but right from the beginning that's what we had. Somehow the "weaponized" took on some kind of special meaning, that this had to be something very different done to it. But if you're going to make anthrax to use as an agent, as a potential aerosol, this is what you do.

How likely is it that smallpox would be used as a bioweapon?
DAH: I think it's unlikely in one sense, less likely than anthrax. I think it is more difficult to get ahold of the virus itself. It is more difficult to manufacture than anthrax. Every step of the way it's that much more difficult than anthrax. But the risk as we see it is not zero. That's the problem. Should an outbreak get started, this could be really quite serious. I think about 70 to 80 percent of the population is susceptible.

But you're against immediate smallpox vaccination of every American?
DAH: One in a thousand will have complications of some sort, and deaths will be about two per million. We'll have also about two per million who will have neurological damage. This is not inconsequential.

Is it a good idea to stockpile 300 million doses of smallpox vaccine?
DAH: I think the idea of stockpiling the vaccine is very good. What is the proper figure I don't know.

As the man who led the smallpox eradication effort, does it enrage you that you have to worry about this?
DAH: Yeah. There's a feeling of immense disappointment that this happened, and at the same time, of betrayal on the part of the Russians. In the most ugly way. I still get angry as I think about it because the Russians actually played a major role in the eradication program. Throughout the program, they provided 25 million doses per year of the vaccine. Without that amount of vaccine, we never would have succeeded.

The Russians were able to produce tons of smallpox virus per year. Is it all accounted for?
DAH: More important than that, perhaps, is the fact [that] the technique for producing large quantities of smallpox virus, of course, rests in the minds of a number of people who have worked there. Half or more of the scientists have left the laboratories. Some have gone to the United States, some have gone to other places in Europe, some have gone to countries that have been involved in terrorist activities. If it hadn't been for the Soviet program, we would not be where we are today in regards to biological weapons.

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