The Real Threat of Ricin
Mail-based bioterror attacks made headlines last week when traces of ricin, a poison derived from the castor bean and a common by-product of castor oil, was found in letters addressed to President Barack Obama, Mississippi Republican Sen. Roger Wicker and Lee County, Miss., Justice Court Judge Sadie Holland, according to reports from the Associated Press.
Ricin, categorized as a “Class B” threat by the Centers for Disease Control and Prevention (CDC), is a non-contagious poison that “kills over time,” according to David Sanders, associate professor of biological sciences at Purdue University.
“Ricin works (as a poison) because it has two proteins linked together. One of the proteins binds to sugars, on the surface of a cell, and there is a chemical bond that links those proteins,” Sanders said.
Ricin becomes toxic when this disulfide bond is broken and it enters the cell, he added. “Ricin interacts with (the cell’s) ribosome and acts as an enzyme, removing one tiny, specific, but important, part of the ribosomal RNA.”
A ribosome is the cell’s factory for producing proteins, and when the cell is intoxicated and exposed to the poison, ribosomes no longer work to synthesize proteins. “That’s how ricin kills over time,” he said.
Sanders added that he agreed with the CDC’s “Class B” level for ricin. “Whenever I discuss (biological weapons) I divide them into three categories,” Sanders said. “True biological agents make more of themselves, and ricin can’t. Anthrax, for example, is a biological agent but only barely. It makes more of itself, but it isn’t transmitted from one human to another, you have to be directly exposed.”
Sanders’ highest personal classification, what he calls “true biological viruses,” include Ebola virus, which is an agent that not only makes more of itself, but is also transmitted from one human to another.
“Without the ability to replicate, ricin is not classified as such a dangerous weapon, so the level of threat is not as substantial,” he said.
Sanders speculated that despite its lack of communicable threat, ricin is still used as a bioterror agent because it is widely available from a natural source. “It is lethal. It can be effective. There are historical examples of its successful – and unsuccessful – use.”
Initial AP reports indicated that the ricin traces found on the letters were “not weaponized,” which Sanders attributed to the grain size of the powder.
“When weaponizing ricin, the finer the grain, the more likely it is to be spread or inhaled, causing more damage,” Sanders said. “So ricin is only ‘weaponized’ when it is in that finely grained state.”
In Monday’s testimony at the hearing of the Mississippi man accused of mailing the poisoned letters, FBI Agent Brandon Grant testified that lab analysis showed the ricin was “in a crude form that could have been created by grinding castor beans in a food processor or coffee grinder,” according to the AP.
Secondary lab analysis was crucial to confirming that the substance on the letters was indeed ricin, because experts agree that some substances can give off an initial false positive for ricin.
“When you do these types of analyses, you do something quick and cheap and that gives you an indication, and then you do something more expensive, and more precise, so you can confirm that it is a specific object,” said Sanders, who was not involved in the testing for this case. “It is that sort of initial, quick and easy analysis that often leads to false positive tests.”
What has now been officially confirmed as ricin on the three letters did not cause a medical threat to Obama or Wicker, whose letters were intercepted at post offices, according to the AP.
However, the AP reported that Holland, whose letter was received in person at her home, was “undergoing medical tests” last week.
Sanders said that typical response to ricin poisoning includes tissue damage and an inflammatory response. “There is currently no particular treatment, so if someone was subjected to inhalation, (medical professionals) would be looking for a problem that could ensue after exposure,” he said. “It’s too late to intervene after (ricin) attacks the ribosome. Once it’s done that, the active component is an enzyme that will attack all ribosomes in a cell. When that happens, it’s an irreversible process.”
What medical professionals can do, he said, is find “a potential place for intervention,” an opportunity to interfere with the cellular components necessary for the toxin or biological agent to be effective. “I would focus research on how those two proteins get separated. There’s a reduction of the disulfide bond, when ricin is reduced by cellular processes, that is a necessary step for it to be activated. It could be possible to create a counter agent to stop that process.”
Sanders also cautioned against panic and fear in face of this bioterrorist threat.
“Sociologically, we need to focus on the fact that the point of this was to create terror and cause panic,” he said. “That’s how these sorts of agents work. It isn’t necessarily about how many people you kill, but about how much terror you evoke.”
“The most important message we should take from this is that we shouldn’t panic. There are already people working on ricin,” he said. “We need to put panic aside...and continue to pursue finding more about how ricin works.”