Anthrax, Ricin, Smallpox: Which Is the Deadliest Bioterrorism Agent?

In between the Boston Marathon bombings and the devastating explosion in West, Texas, last week, Americans also heard about the interception of several pieces of mail meant for President Obama, Senator Roger Wicker, and a Mississippi judge. All contained ricin, a poison made from castor beans. After 30 years of relative obscurity, ricin was back in the news as a bioterrorism agent.

This potent killer first made headlines back in 1978 when the dissident Bulgarian writer Georgi Markov was murdered with an umbrella as he waited for a bus in London. The umbrella, rigged with a hidden weapon in the tip, injected a poison capsule under the writer’s skin. Very James Bond. 



But ricin’s origins are actually pretty humble: It’s an organic compound in castor beans that’s removed when the beans are processed in castor oil.  Once consumed, ricin enters cells and stops them from making protein, which they need to survive, explains the Centers for Disease Control (CDC). Symptoms usually appear in less than 24 hours and can include—depending on whether ricin was ingested, inhaled, or delivered some other way, as by weaponized umbrella—fever, seizures, fluid in the lungs, and organ failure. Ricin can’t be transmitted person-to-person, but once it enters the body there’s no antidote.  The body will fight the poison’s effects, but if the dose was big enough poisoning will lead to death. 

Fortunately, you can’t poison someone just through skin contact with ricin, so the threat from last week’s letters was probably low. News reports, including CNN, described the poison in the letters as a “loose granular substance,” which would have required the recipient to ingest or inhale traces of the granules to get the desired effect.

The scarier part of this potentially deadly mail delivery is the light it shined on something dreadful about this particular brand of terrorism: Bioterrorism can turn almost anything into a weapon. The CDC defines bioterrorism as “the deliberate release of viruses, bacteria, and other germs (agents) used to cause illness or death.” Instead of bombs bioterrorists use plague; instead of guns they use anthrax. With bioterrorism, the typical instruments we associate with aggression and war are no longer relevant. The source of our fear may be a vial of perfume or a fine white powder—even an umbrella.

So how do we prepare and defend against an attack that could come in a very innocuous—even invisible—form? The model for what we do is similar to how we fight infectious diseases like influenza: For the flu, the CDC coordinates various surveillance operations to monitor illness and creates its weekly FluView report. To prepare for flu outbreaks, the government stockpiles products like vaccines and promotes emergency response preparedness so healthcare workers know exactly what to do if an outbreak happens. For bioterrorism, the Department of Homeland Security runs the National Biosurveillance Integration Center, which watches for trends in high-threat diseases. Homeland Security also works to improve rapid response to these agents by implementing emergency readiness, quarantine, and mass protocols to protect the public in case of an attack. 

The CDC categorizes potential bioterrorism agents by class: Class A—the highest priority—are diseases that can be transmitted between people and have high mortality rates, such as anthrax and smallpox. Class B and Class C aren’t nearly so scary; in fact, they only require enhanced surveillance, not action to protect the public.

The perceived reduced threat for agents that aren’t in Class A points up a paradox about bioterrorism: While bioterrorists successfully turn mundane objects into weapons, the weapons are often better at producing fear than actual fatalities. Ricin, which is a Class B bioterror agent, is actually responsible for only one murder in history—the unfortunate Mr. Markov.

For now, any focus on preparedness will likely be focused on those potentially devastating Class A agents, which in addition to smallpox and anthrax also include botulism, plague, tularemia, and viral hemorraghic fevers, like the Ebola and Marburg viruses. A scary lineup, for sure.

--By Jason Hayes

Are you worried about a bioterrorist attack? What agent do you think is most likely to be used?

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• U.S. Says Terrorists Sewing Bombs Inside Humans

• Ebola: Still the Scariest Virus Out There?

The Disease Daily is created by a team of medical doctors, veterinarians, and public health professionals who believe that infectious disease news should be accessible and comprehensible to everyone. As a publication from HealthMap at Boston Children's Hospital, The Disease Daily has access to real-time reporting of infectious disease events all over the world. While HealthMap alerts thecommunity to the outbreaks, The Disease Daily puts those alerts into context, showing readers the impact of infectious disease on policy, economics, and community.

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