A letter with ricin addressed to the office of Sen. Roger Wicker (R-MS) has been intercepted at a US Capitol off-site mail facility.

The envelope was taken to a lab for testing and the poisonous substance was confirmed to be ricin. Senators have been briefed by administration officials behind closed doors about the incident.

According to the CDC, if authorities suspect people have inhaled ricin, a potential clue would be that a large number of people who had been close to each other rapidly develop fever, cough and excess fluid in their lungs. The symptoms would likely be followed by severe breathing problems and possible death. There is no antidote for ricin.

Since the anthrax letters in late 2001, all mail bound for the Capitol complex goes off-site for testing.