Ricin is a carbohydrate-binding protein (which is called lectins) produced within the seeds of the castor bean plant (Ricinus communis), which is widely spread across tropical regions. Ricin is one of the most toxic substances known, and ingesting as few as two castor seeds can be toxic, and inhaling or injecting as little as five to ten micrograms per kilogram can be lethal. The severity of ricin toxicity depends largely on the route of exposure to the toxin. Inhalation and injection are the most toxic and lethal routes of exposure, followed by oral ingestion.1
Ricin is water-soluble, which means when the seeds are processed into castor oil, the toxic compound is easily separated out.1 This confirms the safety of castor oil, which is widely used for multiple medical purposes (e.g. in laxatives), cosmetics, paints, and varnishes,, as well as in lubricating oils for jet engines, high-speed automotive and industrial machinery.1,2,3
Ricin’s toxicity and mechanism of action
If castor beans are swallowed whole without chewing or maceration, intoxication is reduced because the protective, solid, shell-like coating of the castor bean makes the release of ricin difficult.1 Chewed or crushed seeds as well as immature castor beans are much more toxic than mature intact beans. Ingested ricin is absorbed within two hours via the blood and lymphatic vessels and accumulates in the liver and spleen.1
Ricin is a glycoprotein lectin composed of two chains, termed A and B, linked by a disulphide bond. The B chain is responsible for ricin’s entry into the cytosol (the fluid component inside cells), while the A chain inhibits protein synthesis which in turn leads to cell death.2 Although protein synthesis inhibition is the primary mechanism of ricin’s toxicity, there are other mechanisms, such as triggering apoptotic pathways, direct cell membrane damage, alteration of membrane structure and function, and release of inflammatory cytokines.1,2,3
Ricin: a biological warfare and assassination agent
Ricin has been identified as a potential bioweapon used by the United States and the Soviet Union.2 Since 1918, ricin has been considered for use as a weapon in the US and UK military programs, which have investigated the feasibility of using aerosolized ricin in bombs. Moreover, Iraq reportedly attempted to weaponize ricin in the 1980s.4 The Centres for Disease Control and Prevention (CDC) categorises ricin as a Category B agent (second-highest priority), which is easy to disseminate, resulting in low mortality but moderate to high morbidity. It can be prepared as a powder or solubilised in liquids.1 Deliberate dissemination may occur either through the addition of food or water (by aerosol) or by direct parenteral injection.1
One of the notable historical incidents of deliberate ricin poisoning was that of a Bulgarian journalist, Georgi Markov, which took place in Great Britain in 1978. He was assassinated by an “Umbrella Murder” injection of about 500 micrograms of ricin toxin.3,4 Immediately, he sensed a localized pain at the injection site and then had generalised weakness after five hours. Upon admission to the hospital, symptoms included fever, nausea, vomiting, and tachycardia. The injection site became hardened, and regional lymph nodes became swollen. Over the following days, his heart rate increased to 160 beats per minute, he became hypotensive and leukocytic (having an excess of white blood cells), and his urine output reduced. Consequently, hematemesis and complete atrioventricular conduction block resulted in death.3
In 2013, another incident involving ricin poisoning was revealed when envelopes sent to the US President Obama and a U.S. senator tested positive for ricin.1,3,4
Symptoms of ricin poisoning
Symptoms of ricin toxicity differ according to the route of exposure to the toxin. In the case of ricin ingestion, symptoms appear within a few hours, while in the case of ricin injection or inhalation, symptoms may start immediately or may appear in several hours.
- Ingestion of ricin:
Symptoms usually appear within the first 4-36 hours of ingestion. Mild symptoms include abdominal pain, nausea, vomiting, and diarrhoea.1 However, if the poisoning is severe, the patient can develop hematemesis (internal bleeding, where a person vomits as a result) and melena (black tarry stool caused by bleeding in the upper gastrointestinal (GI) tract).2
These symptoms can eventually progress to hypotension, renal dysfunction, and possibly death.
- Inhalation of ricin:
Symptoms can occur within 8 hours and can include coughing, wheezing, dyspnoea, arthralgia (joint stiffness), fever, sore throat, and congestion.1 If the person remains exposed to the toxin, pulmonary oedema and pneumonia may develop, which can progress to respiratory distress and death.
- Injection of ricin:
Initial symptoms can occur within the first 6 hours, including erythema (a form of skin irritation), blisters, induration (thickening and hardening of the skin) at the injection site, localised necrosis around the injection site, and generalised weakness and myalgia.1 Within 24-36 hours, capillary/vascular leak syndrome and swelling of regional lymph nodes occur, which can potentially lead to hypotension, seizures, multiorgan failure, and death.1,2,3,5
Diagnosing ricin poisoning can often be difficult. Currently, there is no standard and approved method for the detection of ricin toxin. This is due to the lack of specific clinically validated assays (for the detection of ricin in biologic fluids) that can be performed by a healthcare facility/hospital clinical laboratory. There are several nonspecific findings that can indicate ricin poisoning, including:
- Signs of altered liver function
- Signs of altered renal function
- Metabolic acidosis
- Hematuria (presence of blood in urine)
- Leukocytosis (an increased number of leukocytes by two to five-fold)
Moreover, an alkaloid named ricinine is extracted from the same castor bean plant from which ricin is extracted. This means its presence in a biological sample would serve as a marker for the presence of ricin. Hence, tests such as urine assays (able to detect ricinine 48 hours after exposure) are being developed.1 Nevertheless, these are only to confirm exposure rather than for use in initial diagnosis.
Other methods for the detection of ricin include:
- Enzyme-linked immunosorbent assays (ELISA), can detect ricin in animal tissues and fluids.3
- Time-resolved fluorescence immunoassays, which candetectricin-antibody conjugates two weeks after ricin ingestion (in surviving patients).1
- A polymerase chain reaction can be used to identify the presence of the DNA that encodes the ricin protein specifically.1,5
These tests take time to perform and will most likely not be immediately available to assist in initial clinical decision-making.
Treatment and management
There is no cure/antidote for ricin poisoning. Hence, it is important to avoid exposure to ricin. Nevertheless, if exposure took place, decontamination and removal of the source of ricin toxin would be the first action.1 This should be followed by supportive medical care, which helps minimise and manage the effects of ricin poisoning. All symptomatic patients with suspected ricin exposure should be admitted to a hospital to receive immediate treatment.
There are different types of supportive medical care. The most effective type of care would depend on the route of exposure to the toxin and how long ago the exposure took place. Various supportive medical care can be offered, including:
- Correction of fluid and electrolyte imbalances.2
- Monitoring liver and renal functions.2
- Administration of intravenous fluids and vasopressors (like dopamine) for hypotension.1
- Administration of activated charcoal to those who have recently ingested ricin if vomiting has not begun and the airway is secure.1,2
- Gastric lavage if the ingestion has occurred in an hour or less.2
- Offering respiratory support by administering anti-inflammatory drugs and analgesics as well as helping the patients breathe by offering positive-pressure breathing and artificial ventilation.3
- Treatment of seizure, in case of any.2
- Wash out their eyes with water in case of eye irritation.1,2,3
Ricin is a potent cell toxin extracted from the seeds of the castor bean plant. Ricin has been used as a biological warfare and assassination agent due to its stability as well as ease of access and relative ease of extraction. The clinical manifestations of ricin poisoning differ according to the route of exposure: ingestion, inhalation, or injection. Diagnosis of ricin intoxication may not be straightforward. It largely depends on the patient’s clinical manifestation, the laboratory confirmation of ricin exposure, and the clinicians’ suspicion of a credible ricin threat or an outbreak of severe gastrointestinal or respiratory illness. To assist in early diagnosis and prevent further morbidity and mortality, it is important to notify the poison control centres, public health officials and local law enforcement agencies in case of any incident of ricin exposure or outbreak of illness consistent with ricin poisoning.
What to do if I experience symptoms of ricin exposure?
Seek medical attention straight away. While waiting for help, follow these steps:
- Get away from the area where you suspect you were exposed to ricin as fast as possible.
- Take off clothes that might have ricin on them and dipose of them.
- Use a lot of soap and water to rinse skin exposed to ricin.
Is ricin poisoning contagious?
No, it is not, it cannot spread from one person to another.
Can I die from ricin poisoning?
If no medical assistance is not sought promptly, then yes, ricin poisoning may lead to death, especially if the ricin is injected or inhaled. Ingested ricin is not well absorbed through the gastrointestinal tract, so there is more time for proper medical assistance to be given.
- Audi, Jennifer, et al. ‘Ricin PoisoningA Comprehensive Review’. JAMA, vol. 294, no. 18, Nov. 2005, pp. 2342–51. Silverchair, https://doi.org/10.1001/jama.294.18.2342.
- Hayoun, Michael A., et al. ‘Ricin Toxicity’. StatPearls, StatPearls Publishing, 2023. PubMed, http://www.ncbi.nlm.nih.gov/books/NBK441948/.
- Moshiri, Mohammad, et al. ‘Ricin Toxicity: Clinical and Molecular Aspects’. Reports of Biochemistry & Molecular Biology, vol. 4, no. 2, Apr. 2016, pp. 60–65. PubMed Central, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4986263/.
- Ricin: Technical Background and Potential Role in Terrorism, https://www.everycrsreport.com/reports/RS21383.html. Accessed 25 Aug. 2023.
- Ricin, Missouri Department of Health and Senior Services Communicable Disease Investigation Reference Manual, Section 4.0 Diseases and Conditions, 2011, Division of Community and Public Health, https://health.mo.gov/living/healthcondiseases/communicable/communicabledisease/cdmanual/pdf/Ricin.pdf.