Ricin poisoning.

Ricin is a naturally occurring toxin derived from the beans of the castor oil plant Ricinus communis. It is considered a potential chemical weapon. Ricin binds to cell surface carbohydrates, is internalised then causes cell death by inhibiting protein synthesis. Oral absorption is poor and absorption through intact skin most unlikely; the most hazardous routes of exposure being inhalation and injection. Features of toxicity mainly reflect damage to cells of the reticuloendothelial system, with fluid and protein loss, bleeding, oedema and impaired cellular defence against endogenous toxins. It has been estimated that in man, the lethal dose by inhalation (breathing in solid or liquid particles) and injection (into muscle or vein) is approximately 5-10 micrograms/kg, that is 350-700 micrograms for a 70 kg adult. Death has ensued within hours of deliberate subcutaneous injection. Management is supportive. Prophylactic immunisation against ricin toxicity is a developing research initiative, although presently not a realistic option in a civilian context.

Abrin poisoning.

Abrin is a toxic protein obtained from the seeds of Abrus precatorius (jequirity bean), which is similar in structure and properties to ricin. Abrin is highly toxic, with an estimated human fatal dose of 0.1-1 microgram/kg, and has caused death after accidental and intentional poisoning. Abrin can be extracted from jequirity beans using a relatively simple and cheap procedure. This satisfies one criterion of a potential chemical warfare agent, although the lack of large scale production of jequirity seeds means that quantity is unavailable for ready mass production of abrin for weapons. This contrasts with the huge cultivation of Ricinus seeds for castor oil production. At the cellular level, abrin inhibits protein synthesis, thereby causing cell death. Many of the features observed in abrin poisoning can be explained by abrin-induced endothelial cell damage, which causes an increase in capillary permeability with consequent fluid and protein leakage and tissue oedema (the so-called vascular leak syndrome). Most reported cases of human poisoning involve the ingestion of jequirity beans, which predominantly cause gastrointestinal toxicity. Management is symptomatic and supportive. Experimental studies have shown that vaccination with abrin toxoid may offer some protection against a subsequent abrin challenge, although such an approach is unlikely to be of benefit in a civilian population that in all probability would be unprotected.