Be Alert for Ricin Poison Cases After Deadly Toxin Used in Threat

Look for epidemiologic clues to detect clusters

Clinicians should be alert for possible cases of ricin poisoning because the easily available toxin was used recently to make a terrorist threat at mail processing center in Greenville, SC, public health investigators warn.

Ricin poisoning might resemble typical gastroenteritis or respiratory illness, making it difficult to discern from other infections and exposures. Thus, suspicion of cases should occur in conjunction with epidemiologic clues suggestive of a chemical release, the Centers for Disease Control and Prevention (CDC) recommends.1 For example, a ricin attack may lead to an unusual increase in the number of patients seeking care or an unexpected progression of symptoms in a group of patients. With a broad panoply of symptoms somewhat dependent on how the poison was delivered, a ricin attack could go undetected until an astute epidemiologist identifies a cluster of cases, says Martin Belson, MD, a medical toxicologist in the CDC national center for environmental health.

"It’s really difficult because [it] depends on the route that you were exposed," he says. "If you breathe it in, you basically can have flulike symptoms. If you ingest it, it will be like a stomach virus. Of course, it is going to depend again on how much [ricin] and the grade of it. If you start seeing a lot of people with these type of symptoms, especially if they progress beyond your typical viral infection, then you need to be [suspicious]. You have to at least think about it if you see a cluster of people who have similar disease. Of course, with this particular threat associated with it, that has got to raise the bar even more."

The Greenville incident is the most recent example among several documented instances of ricin used as a criminal or terrorist weapon. On Oct. 15, 2003, an envelope with a threatening note and a sealed container was received at a mail processing and distribution facility. Laboratory testing at the CDC confirmed that the substance in the container was ricin. The accompanying note threatened to poison water supplies if demands were not met.

According to published reports, the threat specifically related to new federal regulations over the trucking industry.

"This is someone supposedly domestic that is making this threat," Belson says. "We have known for a long time that countries like Iraq have produced ricin. Before this event, it has always been thought of as some way-off potential. This brings to light that this is a commonly available [material], and it can be very toxic if used in the wrong way in the wrong hands."

Poison from a common plant

Ricin is a biologic toxin derived from the innocuous castor bean plant Ricinus communis. Ricin is one of several toxalbumins that create toxicity in the body by inhibiting protein synthesis in eukaryotic cells. Castor beans are processed throughout the world to make castor oil, and ricin is part of the waste "mash" produced when the oil is processed. The plant is not uncommon.

"I saw one the other day in somebody’s yard driving home." Belson says. "The castor bean is something you can get a hold of rather easily. You can produce it very crudely just by crushing the beans, and apparently this [Greenville case] was fairly crude-looking. It did not look like a purified sample of ricin. But there is not a capability at this time — hopefully, there will be in the near future — to actually detect how purified it is. It is more [a matter of] looking at it visually."

Indeed, no methods are available for the detection of ricin in biologic fluids. Ricinine is a separate compound from ricin present in the castor bean and might be more feasible to monitor in those exposed to ricin-containing plant material, the CDC advises. Treatment for ricin toxicity is primarily supportive, including intravenous fluids, vasopressors, respiratory support, and cardiac monitoring. No specific antidotal therapy exists, and ricin cannot be removed by dialysis. Prophylactic vaccine and immunotherapy are not available. The same general guidelines for gastrointestinal decontamination employed for other ingested toxins should be applied to ricin, the CDC recommends.2

A single dose of activated charcoal should be administered as soon as possible if the patient is suspected of ricin ingestion and is not vomiting. Skin decontamination — preferably in a designated area outside the main emergency department (ED) — should be performed if a powder or similar substance is found on the ricin-exposed patient.

Casting a wide net

In the Greenville case, CDC investigators closed the facility for investigation, but found no evidence of environmental contamination and no cases of ricin-associated illness. The CDC cast a wide net, asking area EDs, clinicians, health departments, and the local postal facility to report any cases consistent with ricin exposure. State poison control center records and intensive care unit charts at seven hospitals in the Greenville, Spartanburg, and Anderson areas were reviewed daily for illness consistent with ricin exposure. Investigators interviewed all 36 workers at the postal facility to identify ricin-related illnesses.

The CDC conducted environmental assessment and sampling at the postal facility, taking 70 wipe samples and five surface dust samples. Wipe samples were collected from specific surfaces in the facility, including storage bins, surfaces, conveyor belts, and sorting tables that had been in contact with the letter. All environmental samples were negative for ricin.

In addition, investigators monitored call volumes at 62 of the 63 poison control centers in the United States for clinical effects consistent with ricin poisoning and for cases referring to the specific product code ("Contaminated Water") because water had been stated as the target by the note in the package. The postal facility was reopened after the environmental samples for ricin were found to be negative and all of the workers were confirmed to be well. In regard to the specific threat in the Greenville case, poisoning a large water reservoir would be no small undertaking, but an attack on the "end-user" water supply would be less subject to dilution. "It would be difficult, but it depends on how much ricin, the purity of the ricin, and the water supply you are talking about," Belson says.

Ricin poisoning is not contagious, and person-to-person transmission does not occur. However, it would be a mistake to underestimate its potential as a bioterrorism weapon, Belson warns.

"Certainly it is psychological, but it is a real threat, too," he says. "This is a compound that is relatively water soluble, and if you really had it refined, you could put it food or water. It doesn’t have much taste, and it is very toxic."

Large amount needed for mass attack

Routes of exposure to ricin include ingestion, inhalation, injection, skin, and eyes. However, systemic toxicity has been described in humans only after ingestion or injection. Ricin is considered to be a much more potent toxin when inhaled or injected compared with other routes of exposure. Processed and purified ricin can be disseminated by aerosol, contamination of food or water, or injection, the CDC reports. No inhalational cases occurred at the postal facility, in part, because the ricin apparently never escaped the container.

"This was not like [anthrax] powder that was being spread to other letters," Belson says. "The ricin material itself was in a sealed container, which was within the envelope with a threat letter."

Airborne spread would be possible if ricin is processed to a small particle size. Ricin particles of less than 5 µ have been used for aerosol dispersion in animal studies and can stay suspended in undisturbed air for several hours, the CDC reports.

"It certainly would be possible," Belson says. "There are a lot of factors, probably most importantly, how pure the ricin is and the size of the particles. Just crushing castor beans would make exposure by aerosolization very unlikely. Ingestion is typically the more concerning route when you just crush beans. You would have to your act together to disperse it broadly and aerosolize it into a large population."

Bioterrorism researchers have found that a large amount of ricin is necessary to produce the desired effect of a mass casualty weapon. For example, the amount of ricin necessary to cover a 100 km2 area and cause 50% lethality, assuming aerosol toxicity of 3 mcg/kg and optimum dispersal conditions, is approximately 4 metric tons. Only 1 kg Bacillus anthracis is required for the same effect.3

"Ricin, however, would have efficacy as a disabling agent," the researchers note. "Its use as a food and water contaminant easily could incapacitate many and overwhelm local health care resources."

Gary Evans is the editor of Bioterrorism Watch. This article was published in the January 2004 issue.


1. Centers for Disease Control and Prevention. Investigation of a ricin-containing envelope at a postal facility — South Carolina. MMWR 2003; 52(46):1,129-1,131.

2. Chyka PA, Seger D. Position statement: Single-dose activated charcoal. American Academy of Clinical Toxicology; European Association of Poisons Centres and Clinical Toxicologists. J Toxicol Clin Toxicol 2000; 38:721-41.

3. Mirarchi FL, Allswede M. CBRNE Ricin. Web: