Castor Bean

The castor bean is a flowering plant that has been favored by breeders and horticulturalists as an ornamental shrub; while not native to the Americas, it can often be seen in parks and public arrangements or as an invasive species in warmer latitudes. The flowers, leaves, and fruits can come in many different colors.

The so-called "bean" is the seed of the fruit; it is shiny and brown, with tan-yellow mottling, and contains the infamous ricin, a lectin protein that easily crosses cell membranes and acts as a potent ribosomal poison. It depurinates an adenine in a highly-conserved rRNA sequence (the "sarcin-ricin loop"), resulting in failure to bind elongation factors — and thus inactivation of the ribosome. Due to its incredible potential for lethality, and the ready availability of the source, ricin has been used in assassinations and has been implicated in terrorist plots and attempts.

Presentation:

The symptomatology of ricin toxicity varies depending on the mode of introduction — ingestion, inhalation, injection, or ocular — and results from inhibition of protein synthesis.

Ingestion (of the seed itself, rather than prepared ricin) is the most common route; patients present after several hours to days with signs of mucosal damage — abdominal pain, diarrhea, nausea and vomiting, and dysphagia; followed by melena and hematemesis. If fluid losses are severe (usually only with higher doses), hypovolemic shock with renal and hepatic damage, electrolyte abnormalities, and altered mental status, followed by death, may ensue.

Inhalation of ricin has not been documented in humans, but has been studied in primate models. Patients would theoretically present in the first several hours with cough, shortness of breath, and fever; which may progress to respiratory distress followed by respiratory failure and death.

Intramuscular/subcutaneous injection of ricin has only been confirmed in a limited number of cases. Patients initially present with generalized weakness, malaise, arthralgias, and myalgias; multi-organ damage follows after several hours, and death may result from hepatorenal and cardiopulmonary failure. Intravenous injection of ricin was studied in the setting of a clinical trial for a ricin-component-containing immunotherapy; dosing was limited by "vascular leak syndrome" in many patients, leading to hypoalbuminemia and generalized edema, pulmonary edema and pleural effusion, and cardiorenal failure; 12 patients required cessation of experimental treatment, and 2 patients died.

In primate models, ocular exposure to ricin led to severe pseudomembranous conjunctivitis.

As an aside, exposure to other compounds in the castor bean — inhaled or topical — can lead to an allergic response up to and including anaphylaxis.

Management:

If not elicited in the history, diagnosis of ricin poisoning may be difficult. Detection of anti-ricin antibodies or ELISA is possible, but is of limited use in the ED setting.

In general, ingestions, inhalations, and injections of ricin are managed supportively. Cardiac, pulmonary, renal, and hepatic function should be monitored and any dysfunctions should be managed conventionally (e.g. fluid resuscitation and vasopressors for hypovolemic shock; or CPAP or mechanical ventilation for respiratory failure).

For ingestions, the utility of decontamination with activated charcoal or gastrointestinal lavage is uncertain as patients usually present several hours after the time of ingestion. Treatment should specifically include replacement of gastrointestinal fluid and electrolyte losses.

There has been some interest in ricin prophylaxis using inhaled or intravenous toxoid to stimulate an immune response. The RiVax vaccine demonstrated short-term efficacy in a limited human-murine trial, but has stagnated in development. Murine trials have also demonstrated the potential therapeutic efficacy of injection of anti-ricin antibody within 2 hours of exposure; however, this is not a treatment that can be made available in any reasonable timeframe.