Ricin Toxicity

Earn CME/CE in your profession:

Continuing Education Activity

Ricin is a naturally occurring carbohydrate-binding protein produced in the seeds of ricinus communis, the plant that produces castor oil. It is toxic when inhaled, ingested, or injected. As few as five to ten micrograms per kilogram can be lethal. This activity reviews the evaluation and management of patients effected by ricin toxicity, and highlights the role of the interprofessional team in caring for these patients.


  • Explain the pathophysiology of ricin.
  • Outline the symptoms and presentation of patients exposed to ricin.
  • Summarize appropriate diagnostic testing and medical management of patients exposed to ricin.
  • Explain the importance of collaboration and communication amongst the interprofessional team as well as public health officials, law enforcement agencies, members of the media, and elected officials to ensure appropriate treatment of patients exposed to ricin and management of incidents involving ricin.


Ricin is a naturally occurring carbohydrate-binding protein produced in the seeds of Ricinus communis, the castor oil plant. It is toxic when inhaled, ingested, or injected. As few as five to ten micrograms per kilogram can be lethal.


Ricin is a lectin (carbohydrate-binding protein) produced in the endosperm of the seeds of the castor oil plant. Ingestion of as few as two castor oil plant seeds has been shown to be toxic, although patients have survived ingesting as many as 30. Ricin is also toxic by inhalation or injection, and as little as five to ten micrograms per kilogram by inhalation can be lethal. Ricin was developed as a biological weapon by both the United States and the Soviet Union. The castor oil plant grows in the wild in tropical climates. Approximately two million tons of castor seeds are produced yearly around the globe. Castor seeds can be crushed to extract castor oil, which has industrial applications in lubricants, dyes, preservatives, and pharmaceuticals. The waste mash of castor seeds after the oil extraction process is approximately 5% ricin by weight. This waste can be detoxified and used as a fertilizer or as a supplement in animal feed. [1] [2]


If a group was targeted as part of a ricin attack, the presentation of some patients with a history of being at a particular place at the same time and complaining of similar symptoms consistent with the route of exposure would likely be the first epidemiologic red flag. Sudden onset of respiratory distress among several people in one place would evidence of aerosol exposure. Nausea, vomiting, and gastrointestinal hemorrhage would common in an ingestion exposure. [1]


Ricin is a globular glycoprotein that is composed of different protein chains connected by a disulfide bond. It is classified as a Type II ribosome-inactivating protein (RIP). The ricin toxin A chain inactivates ribosomes by hydrolyzing the N-glycosidic bond of an adenosine residue in the 28 S ribosomal RNA of eukaryotic cells; this inhibits protein synthesis by blocking the binding of elongation factors. This inhibition of protein synthesis by the ricin toxin A chain is a mechanism of ricin toxicity. The ricin toxin B chain binds to carbohydrates on the surface of eukaryotic cells and facilitates entry of the toxin into the cell. Ricin can enter the cell by numerous mechanisms including both receptor-mediated and adsorptive-mediated endocytosis. After endocytosis, ricin is transferred by vesicular transport from early endosomes to the trans-Golgi network, then undergoes retrograde vesicular transport through the Golgi apparatus. Ricin has been shown to be transported from the Golgi apparatus to the endoplasmic reticulum by the chaperone protein calreticulin. Once ricin reaches the endoplasmic reticulum, the disulfide bond between the A chain and the B chain is reduced by protein disulfide isomerase. The A chain then undergoes partial unfolding, after which it crosses the endoplasmic reticulum membrane via the Sec61p translocon. The unfolded A chain avoids ubiquitination because of its low lysine content, thus enabling the A chain to evade degradation by proteasomes and refold into its biologically active conformation, after which it resumes catalytic activity. [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]


Ricin toxin A chain can inactivate approximately 1500 ribosomes per minute. There are reports that a single molecule of ricin reaching the cytosol can be lethal to a cell. The lethal oral dose by ingestion in humans is estimated to be one to twenty milligrams per kilogram. As little as five to ten micrograms per kilogram by inhalation can be lethal. [21] [22] [23] [7] [8] [9] [10] [15] 

History and Physical

Symptoms of ricin ingestion include nausea, vomiting, diarrhea, hematemesis, and melena. Necrosis of the spleen, liver, and kidneys may occur. Inhalation exposure symptoms include a cough, wheezing, dyspnea, sore throat, and congestion. Exposed patients may go on to develop pulmonary edema and pneumonia. Symptoms of injection exposure include erythema, induration, blisters, capillary leak syndrome, and localized necrosis surrounding the injection site. These symptoms may progress to seizures, shock, organ failure, pulmonary edema, and respiratory failure. Symptoms may begin within a few hours if ingested; however, symptoms may start almost immediately or may not be apparent for several hours in cases of ingestion or inhalation. [4]


Laboratory testing for ricin includes liquid chromatography-mass spectrometry and immunoassays. Laboratory studies may show leukocytosis, electrolyte abnormalities, liver failure, renal failure, and coagulopathy. Chest radiography may be normal or may show pulmonary edema or pneumonia in people with inhalational exposure. [24] [25] [26] [27] [28] [29] [30]

Treatment / Management

All symptomatic patients with suspected ricin exposure should be admitted. The treatment of ricin toxicity is supportive and includes management of shock, correction of electrolyte abnormalities, respiratory support, and treatment of seizures. Patients exposed to ricin by inhalation may require airway management and positive-pressure ventilation. Activated charcoal can be given to patients who have ingested ricin if vomiting has not yet occurred and the patient's airway has been secured. Gastric lavage can be used if the patient ingested ricin within the past hour. Electrolytes, coagulation studies, renal function, and liver function should be monitored; coagulopathies and electrolyte abnormalities should be corrected. There is no ricin antidote available for humans. [31] [32] [33] [34]

Differential Diagnosis

  • Cellulitis
  • Chemotherapeutic drugs
  • Capillary leak syndrome
  • CBRNE-Staphylococcal enterotoxin B
  • Myocardial infarction
  • Pneumonia
  • Plagues
  • Phosgene toxicity
  • Q fever
  • Salmonella infection
  • Shigella infection
  • Streptococcus aurea infection
  • Tularemia
  • Undifferentiated sepsis

Pearls and Other Issues

Ricin was used in the assassination of Bulgarian dissident Georgi Markov in London in 1978; a pellet containing ricin was found in his leg during an autopsy. A Bulgarian defector, Vladimir Kostov, survived a similar assassination attempt in Paris involving the injection of a pellet containing ricin under his skin ten days prior. In August 1981, double-agent Boris Korczak survived being shot by an air gun with a pellet containing ricin while at a grocery store in Virginia. In 2003, ricin was detected in a facility that handled mail for the White House. However, no one was harmed. In April 2013, envelopes addressed to President Barack Obama, Mississippi Senator Roger Wicker, and Lee County, Mississippi Judge Sadie Holland tested positive for ricin; Tupelo, Mississippi, resident Everett Dutschke was arrested later that month and plead guilty in May 2014. In May 2013, actress Shannon Richardson mailed letters containing ricin to President Barack Obama, New York City Mayor Michael Bloomberg, and Mark Glaze, who at that time was executive director of Mayors Against Illegal Guns. All suspected cases of ricin exposure should be reported to poison control and the health department. Ricin is included on the United States Department of Health and Human Services Select Agents and Toxins List under 42 CFR 73.3. [35] [36] [34]

Enhancing Healthcare Team Outcomes

Recent use of ricin demonstrates how incidents involving ricin will quickly become international news. Once a patient has been poisoned with ricin, healthcare providers will be responsible for communicating not only numerous colleagues and staff but also with public health officials, law enforcement agencies, members of the media, and elected officials. In attacks involving numerous numbers of casualties or high-profile targets such as elected officials, the marshaling of resources to respond will almost certainly reach the national level. (Level V)

Important interprofessional communication points early in the care of the patient among physicians, nurses, and pharmacists will include adequate decontamination of the patient and appropriate precautions for first responders and hospital staff to avoid additional casualties. Training and education prior to such an event will be more effective than just-in-time training after an event has occurred when emotions run high and resources may run low. In large-scale events, it will be essential for healthcare staff to have a clear understanding of their available resources as well as the anticipated demands on those resources, and continuously communicating with government officials to access medical supply stockpiles and resources for the capacity to treat large numbers of patients will be vital. (Level V)

Article Details

Article Author

Michael A. Hayoun

Article Author

Erwin L. Kong

Article Author

Matthew E. Smith

Article Editor:

Kevin C. King


7/18/2022 11:40:37 PM

PubMed Link:

Ricin Toxicity



[Today's threat of ricin toxin]., From S,PÅ‚usa T,, Polski merkuriusz lekarski : organ Polskiego Towarzystwa Lekarskiego, 2015 Sep     [PubMed PMID: 26449579]


Toxins as Weapons: A Historical Review., Pita R,Romero A,, Forensic science review, 2014 Jul     [PubMed PMID: 26227025]


Potential therapeutic applications of plant toxin-ricin in cancer: challenges and advances., Tyagi N,Tyagi M,Pachauri M,Ghosh PC,, Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine, 2015 Nov     [PubMed PMID: 26349746]


Clinical and Pathological Findings Associated with Aerosol Exposure of Macaques to Ricin Toxin., Pincus SH,Bhaskaran M,Brey RN 3rd,Didier PJ,Doyle-Meyers LA,Roy CJ,, Toxins, 2015 Jun 9     [PubMed PMID: 26067369]


RTB Lectin: a novel receptor-independent delivery system for lysosomal enzyme replacement therapies., Acosta W,Ayala J,Dolan MC,Cramer CL,, Scientific reports, 2015 Sep 18     [PubMed PMID: 26382970]


Neutralizing monoclonal antibodies against ricin's enzymatic subunit interfere with protein disulfide isomerase-mediated reduction of ricin holotoxin in vitro., O'Hara JM,Mantis NJ,, Journal of immunological methods, 2013 Sep 30     [PubMed PMID: 23774033]


Neutralizing Monoclonal Antibodies against Disparate Epitopes on Ricin Toxin's Enzymatic Subunit Interfere with Intracellular Toxin Transport., Yermakova A,Klokk TI,O'Hara JM,Cole R,Sandvig K,Mantis NJ,, Scientific reports, 2016 Mar 7     [PubMed PMID: 26949061]


Retrograde transport of ricin., Wesche J,, International journal of medical microbiology : IJMM, 2002 Feb     [PubMed PMID: 11890552]


An interaction between ricin and calreticulin that may have implications for toxin trafficking., Day PJ,Owens SR,Wesche J,Olsnes S,Roberts LM,Lord JM,, The Journal of biological chemistry, 2001 Mar 9     [PubMed PMID: 11113144]


Reductive activation of type 2 ribosome-inactivating proteins is promoted by transmembrane thioredoxin-related protein., Pasetto M,Barison E,Castagna M,Della Cristina P,Anselmi C,Colombatti M,, The Journal of biological chemistry, 2012 Mar 2     [PubMed PMID: 22228764]


Protein disulphide-isomerase reduces ricin to its A and B chains in the endoplasmic reticulum., Spooner RA,Watson PD,Marsden CJ,Smith DC,Moore KA,Cook JP,Lord JM,Roberts LM,, The Biochemical journal, 2004 Oct 15     [PubMed PMID: 15225124]


Reductive activation of ricin and ricin A-chain immunotoxins by protein disulfide isomerase and thioredoxin reductase., Bellisola G,Fracasso G,Ippoliti R,Menestrina G,Rosén A,Soldà S,Udali S,Tomazzolli R,Tridente G,Colombatti M,, Biochemical pharmacology, 2004 May 1     [PubMed PMID: 15081871]


The isolation and characterization of temperature-dependent ricin A chain molecules in Saccharomyces cerevisiae., Allen SC,Moore KA,Marsden CJ,Fülöp V,Moffat KG,Lord JM,Ladds G,Roberts LM,, The FEBS journal, 2007 Nov     [PubMed PMID: 17916187]


The N-terminal ricin propeptide influences the fate of ricin A-chain in tobacco protoplasts., Jolliffe NA,Di Cola A,Marsden CJ,Lord JM,Ceriotti A,Frigerio L,Roberts LM,, The Journal of biological chemistry, 2006 Aug 18     [PubMed PMID: 16774920]


Saporin and ricin A chain follow different intracellular routes to enter the cytosol of intoxicated cells., Vago R,Marsden CJ,Lord JM,Ippoliti R,Flavell DJ,Flavell SU,Ceriotti A,Fabbrini MS,, The FEBS journal, 2005 Oct     [PubMed PMID: 16176271]


Ricin. Mechanisms of cytotoxicity., Lord MJ,Jolliffe NA,Marsden CJ,Pateman CS,Smith DC,Spooner RA,Watson PD,Roberts LM,, Toxicological reviews, 2003     [PubMed PMID: 14579547]


Ricin trafficking in cells., Spooner RA,Lord JM,, Toxins, 2015 Jan 9     [PubMed PMID: 25584427]


The mechanism of action of ricin and related toxic lectins on eukaryotic ribosomes. The site and the characteristics of the modification in 28 S ribosomal RNA caused by the toxins., Endo Y,Mitsui K,Motizuki M,Tsurugi K,, The Journal of biological chemistry, 1987 Apr 25     [PubMed PMID: 3571242]


The RNA N-glycosidase activity of ricin A-chain. The characteristics of the enzymatic activity of ricin A-chain with ribosomes and with rRNA., Endo Y,Tsurugi K,, The Journal of biological chemistry, 1988 Jun 25     [PubMed PMID: 3288622]


The low lysine content of ricin A chain reduces the risk of proteolytic degradation after translocation from the endoplasmic reticulum to the cytosol., Deeks ED,Cook JP,Day PJ,Smith DC,Roberts LM,Lord JM,, Biochemistry, 2002 Mar 12     [PubMed PMID: 11876649]


Toxicity of ricin A chain is reduced in mammalian cells by inhibiting its interaction with the ribosome., Jetzt AE,Li XP,Tumer NE,Cohick WS,, Toxicology and applied pharmacology, 2016 Nov 1     [PubMed PMID: 27639428]


Meneguelli de Souza LC,Carvalho LP,Araújo JS,Melo EJT,Machado OLT, Cell toxicity by ricin and elucidation of mechanism of Ricin inactivation. International journal of biological macromolecules. 2018 Jul 1     [PubMed PMID: 29522821]


Liu WY, Research on ribosome-inactivating proteins from angiospermae to gymnospermae and cryptogamia. American journal of translational research. 2017     [PubMed PMID: 29312524]


Recommended Immunological Assays to Screen for Ricin-Containing Samples., Simon S,Worbs S,Avondet MA,Tracz DM,Dano J,Schmidt L,Volland H,Dorner BG,Corbett CR,, Toxins, 2015 Nov 26     [PubMed PMID: 26703725]


Characterization of Ricin and R. communis Agglutinin Reference Materials., Worbs S,Skiba M,Söderström M,Rapinoja ML,Zeleny R,Russmann H,Schimmel H,Vanninen P,Fredriksson SÅ,Dorner BG,, Toxins, 2015 Nov 26     [PubMed PMID: 26703723]


Point-of-care diagnostics for ricin exposure., Diakite ML,Rollin J,Jary D,Berthier J,Mourton-Gilles C,Sauvaire D,Philippe C,Delapierre G,Gidrol X,, Lab on a chip, 2015 May 21     [PubMed PMID: 25892365]


Ricin detection: tracking active toxin., Bozza WP,Tolleson WH,Rosado LA,Zhang B,, Biotechnology advances, 2015 Jan-Feb     [PubMed PMID: 25481398]


Evaluating 6 ricin field detection assays., Slotved HC,Sparding N,Tanassi JT,Steenhard NR,Heegaard NH,, Biosecurity and bioterrorism : biodefense strategy, practice, and science, 2014 Jul-Aug     [PubMed PMID: 24978020]


Mass spectrometric detection of protein-based toxins., Tevell Åberg A,Björnstad K,Hedeland M,, Biosecurity and bioterrorism : biodefense strategy, practice, and science, 2013 Sep     [PubMed PMID: 23971809]


Yeast Reporter Assay to Identify Cellular Components of Ricin Toxin A Chain Trafficking., Becker B,Schnöder T,Schmitt MJ,, Toxins, 2016 Dec 6     [PubMed PMID: 27929418]


Ricin: current understanding and prospects for an antiricin vaccine., Marsden CJ,Smith DC,Roberts LM,Lord JM,, Expert review of vaccines, 2005 Apr     [PubMed PMID: 15889996]


Insertional mutagenesis of ricin A chain: a novel route to an anti-ricin vaccine., Marsden CJ,Knight S,Smith DC,Day PJ,Roberts LM,Phillips GJ,Lord JM,, Vaccine, 2004 Jul 29     [PubMed PMID: 15246614]


Suicidal death after injection of a castor bean extract (Ricinus communis L.)., Coopman V,De Leeuw M,Cordonnier J,Jacobs W,, Forensic science international, 2009 Aug 10     [PubMed PMID: 19477090]


Ricin as a weapon of mass terror--separating fact from fiction., Schep LJ,Temple WA,Butt GA,Beasley MD,, Environment international, 2009 Nov     [PubMed PMID: 19767104]


Investigation of a ricin-containing envelope at a postal facility--South Carolina, 2003.,, MMWR. Morbidity and mortality weekly report, 2003 Nov 21     [PubMed PMID: 14627953]


Modern toxic antipersonnel projectiles., Gaillard Y,Regenstreif P,Fanton L,, The American journal of forensic medicine and pathology, 2014 Dec     [PubMed PMID: 25354227]