Roger Wicker's office is pictured. | AP Photo

Sen. Wicker's office was closed off on Tuesday evening.

What is ricin?

Here are some basic facts about ricin, drawn from the Centers for Disease Control and Prevention.

Q: What is ricin?

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A: It’s a highly potent poison found naturally in castor beans — which can safely be made into castor oil. Ricin is a part of the waste “mash” from making the oil and can be a powder, a mist or a pellet. Chewing castor beans can also release the harmful substance.

Q: How does exposure occur?

A: Other than ingesting beans, the CDC says “it would take a deliberate act to make ricin and use it to poison people.” Unintentional exposure is unlikely.

( Also on POLITICO: Letter sent to Wicker tests positive for ricin)

Q: Is it contagious?

A: No. Someone who becomes sick from ricin can’t spread it through casual contact. However, touching ricin on someone’s body or clothes can be dangerous.

Q: What are the signs and symptoms of exposure?

A: It depends on the means of exposure — ingestion, inhalation, injection or through the skin and eyes. (It isn’t usually absorbed through normal skin contact, but if ricin were on someone’s hand that person may end up ingesting it.) It can cause respiratory, gastrointestinal and circulatory symptoms and can lead to death 36 to 72 hours after exposure.

Q: Is there a cure?

A: There is no antidote, but victims can get supportive medical care in an attempt to minimize the effects of poisoning.

Q: Has it ever been used as a weapon?

A: Remember Georgi Markov, the Bulgarian writer attacked with an umbrella in London in 1978? The umbrella injected a poison ricin pellet under his skin. It killed him.

The U.S. military experimented with using ricin in the 1940s, and there have been some reports that it was used by Iraq in the 1980s or by terrorist organizations.