This document describes the characteristics of ricin toxin.
Ricin toxin, found in the bean of the castor plant, Ricinis communis, is one of the most toxic and easily produced plant toxins. The toxicity of castor beans has been known since ancient times, and more than 750 cases of intoxication in humans have been described. Although ricin's lethal toxicity is approximately 1,000-fold less than that of botulinum toxin, ricin may have significance as a biological weapon because of its heat stability and worldwide availability, in massive quantities, as a by-product of castor oil production. The clinical signs, symptoms, and pathological manifestations of ricin toxicity vary with the dose and the route of exposure. Ricin is less toxic by oral injection than by other routes, probably because of poor absorption and some enzymatic digestion in the digestive tract. The only information on inhalation of ricin in humans is an allergic syndrome reported in workers exposed to caster bean dust. The clinical picture is characterized by sudden onset of congestion of the nose and throat, itchiness of the eyes, urticaria, and tightness of the chest. In more severe cases, wheezing, leading to bronchial asthma, may also occur, and may last for several hours. Affected individuals respond to symptomatic therapy and removal from the source of exposure. Like other potential intoxications on the unconventional battlefield, epidemiological findings will likely play a central role in diagnosis. Death after inhalation of a lethal dose appears to be caused by hypoxemia resulting from massive pulmonary edema and alveolar flooding. Diagnosis can be confirmed through the use of enzyme-linked immunosorbent assays of tissues or body fluids. Prophylactic administration of an investigational vaccine protects laboratory animals from inhalational and other routes of challenge. 55 references