Ricin, a plant protein toxin derived from the beans of the castor plant, is one of the most toxic and easily produced of the plant toxins. Although the lethal toxicity of ricin is about 1000-fold less than botulinum toxin, the worldwide ready availability of castor beans and the ease with which the toxin can be produced give it significant potential as a biological weapon.

Since ancient times, more than 750 cases of ricin intoxication have been described. Ricin may have been used in the highly published killing of Bulgarian exile Georgi Markov in London in 1978. He was attacked with a device in an umbrella that implanted a ricin-containing pellet into his thigh.

Signs and symptoms

The toxicity of ricin varies greatly with the way it is given. Ricin is extremely toxic to cells and acts by inhibiting protein synthesis. Inhalation exposure causes primarily breathing and lung problems. If eaten, ricin causes symptoms in the GI tract. If injected, the reaction takes place in that area.

  • Following inhalation exposure of ricin, toxicity is characterized by the sudden onset of nasal and throat congestion, nausea and vomiting, itching of the eyes, itching, and tightness in the chest. If exposure is significant, after 12-24 hours severe breathing problems may set in. In animal studies, death occurs 36-48 hours after severe exposure.
  • Ingestion of ricin is generally less toxic because it is not absorbed well and may degrade in the digestive tract. Out of 751 ingestions recorded, only 14 resulted in a death.
  • At low doses, injection exposures produce flulike symptoms, body aches, nausea, vomiting, and localized pain and swelling at the injection site. Severe exposure results in tissue death and GI bleeding, as well as widespread liver, spleen, and kidney problems.

Diagnosis

The diagnosis of ricin poisoning is made on the basis of symptoms and whether exposure was possible. In biological warfare, exposure is likely to occur by inhalation of a toxin aerosol.

Victims may have certain signs on a chest x-ray. The diagnosis can be confirmed by lab tests on samples from a nasal swab. Ricin can be identified for up to 24 hours after exposure.

Treatment

Treatment is mainly to relieve symptoms. If exposure was by inhalation, the person may need help breathing. Those who ingested the poison may need to have their stomachs pumped (gastric lavage), or they might be given activated charcoal to soak up the material.

Prevention

Currently, no vaccine is available for ricin exposure. Test vaccines have proven effective in animals. Other drugs are being studied as well.