Other Biological Agents: Botulism, Plague, Tularemia, HFVs

Last updated January 1, 2006

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Besides anthrax and smallpox, which biological agents are U.S. authorities most worried about?

The bacteria that cause plague and tularemia (the toxin which carries botulism), and hemorrhagic fever viruses (HFVs) such as Ebola and Marburg. The Centers for Disease Control and Prevention think that these agents pose the greatest hazard to public heath, though they may not be the most likely choices for a terrorist attack.

Could terrorist groups use these agents?

Not easily. Precisely because they are so deadly and contagious, these microbes are difficult to work with. In order to cause mass casualties, terrorist groups would also need to develop an effective means of dispersing them through the air, which would be difficult without specialized technical assistance. The agents would have to be converted into tiny particles by a specialized sprayer or milled into a very fine powder, then dispersed in an aerosol. But neither specialized sprayers nor milled, “superfine” versions of these agents are easy to come by.

Terrorists might resort instead to using an agent to contaminate food or beverage supplies, but this method probably wouldn’t inflict mass casualties. Botulinum toxin might be the best candidate for food or beverage contamination, even though it is killed by thorough cooking.

What is botulism?

A potentially fatal but noncontagious disease marked by muscle paralysis. Botulism is caused by exposure to botulinum nerve toxin, the single most toxic substance known to science. Its extraordinary potency has made it one of the most widely researched bioweapons: a single gram of botulinum toxin would theoretically be enough to kill more than a million people, if a lethal dose were administered to each person individually. Clostridium botulinum, the bacterium that produces botulinum toxin, can be found naturally in soil, and the toxin is sometimes present in undercooked food or improperly canned goods.

Botulinum toxin is also the first biological toxin to be approved as a medical treatment: it is used to treat neuromuscular disorders, lower back pain, cerebral palsy, and—marketed as Botox—to temporarily eliminate wrinkles by paralyzing the facial muscles.

What is plague?

An extraordinarily lethal illness caused by the bacterium Yersinia pestis. It takes two main forms:

  • Bubonic plague, the more common and less deadly variant, is carried by rodents and transmitted to humans via flea bites; it cannot spread from person to person. This form of plague caused the Black Death that devastated China, the Middle East, and Europe in the fourteenth century, killing a larger proportion of the world’s population than any single war or epidemic since.
  • Pneumonic plague infects the lungs, travels through the air, and is highly contagious. It’s also rarer and more lethal than bubonic plague. If those infected do not receive treatment, their mortality rate is nearly 100 percent.

What is tularemia?

One of the world’s most contagious diseases. Also known as rabbit fever, it is caused by Francisella tularensis, a rare bacterium carried by small mammals including rabbits and squirrels. Humans typically contract the disease from contact with the tissues or body fluids of infected animals, or from the bites of infected insects.  Tularemia cannot spread from person to person. Experts say that if tularemia bacteria were used as a weapon, it would probably be dispersed in an aerosol, thereby spreading an especially serious, inhaled form of the disease. Although tularemia is less lethal than some agents discussed here, death rates for those infected with the inhaled form can still climb as high as 30 to 60 percent if left untreated.

What are hemorrhagic fever viruses?

A deadly and gruesome class of viruses which produce high fever and leakage from blood vessels, ultimately causing bleeding from internal organs as well as the eyes, ears, nose, and mouth. Hemorrhagic fever viruses (HFVs) are carried by animals in Africa, Asia, the Middle East, and South America. We don’t know exactly how these diseases spread from animals to humans, but once they do, they can be transmitted from person to person via bodily fluids. There are four HFV families, of which filoviruses, including the notorious Ebola and Marburg viruses, and arenaviruses, such as the Lassa virus, are considered the most serious bioterror threats. There is no treatment for Ebola, and up to 90 percent of those who contract the disease die.

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