Factbox - Ricin: deadly, easily concealable poison

April 17 - Ricin, one of the deadliest poisons known, was found in a letter addressed to U.S. President Barack Obama, according to preliminary tests.

Following are some key facts about ricin:

- Ricin is made from castor beans, the same substance used to make castor oil. It can be found as a powder, mist, or pellet and is very difficult to trace.

- Ricin is perhaps best known as the poison used to assassinate Bulgarian exile Georgi Markov in London in 1978.

An agent injected Markov with a ricin pellet using a specially rigged umbrella. Markov died a few days later.

- In the 1940s, the U.S. military experimented with using ricin as a possible warfare agent.

- Symptoms of ricin poisoning may begin within less than 10 hours of exposure. They vary depending on whether it was injected, breathed in, or eaten.

When inhaled, symptoms include difficulty in breathing, fever, cough, nausea, sweating and tightness in the chest. Death occurs after blood pressure plummets and breathing stops.

When swallowed, ricin causes vomiting, diarrhoea, dehydration, low blood pressure, seizures, and blood in the urine. “Within several days, liver, spleen, and kidneys might stop working and the poisoned person could die.

- Ricin prevents bodily cells from making the proteins they need. Death can occur within 36 to 72 hours of exposure.

- There is no known antidote. Treatment includes use of respirators, fluids, flushing the stomach and treating low blood pressure.

Source: the Centres for Disease Control and Prevention

(Reporting by Eric M. Johnson; Editing by Nick Zieminski)