LAS VEGAS, Nevada (CNN) -- A man who stayed in a Las Vegas hotel room where ricin was found is in critical condition at a hospital, where he has been since mid-February, said a Las Vegas Metropolitan Police Department official.
A man is in critical condition after exposure to ricin at a Las Vegas, Nevada, hotel.
Deputy Chief Kathy Suey said the man called from the hotel asking for medical help on February 14, saying he was suffering from respiratory distress, and was transported to the hospital.
Since he was gone from the extended-stay hotel and not paying his rent, managers began eviction procedures, Suey said at a news conference.
A friend or relative of his who came to remove his belongings from the room found the ricin Thursday, she said. Watch Suey describe how the ricin was found »
Tests confirm the substance found in the room was ricin, police said, but it remains a mystery how it got there. Suey said the man hospitalized was not a suspect and police don't know whether the ricin was his, or if he even knew it was there.
The FBI said it was treating the matter as a criminal investigation and terrorism was not suspected.
Pets were found in the room, Suey said. "Two of those pets are fine. One of the pets is deceased or was put down," she said.
There was no evidence that the animal died from ricin exposure, Suey said. "The dog that was in there was without food and water for a week."
She said the man was unable to speak to police, but a doctor at the briefing said he held out hope the man might recover enough to provide information.
"Usually, if [ricin victims] survive the first three to five days, they usually do fine," said Dr. Lawrence Sands of the Southern Nevada Health District, emphasizing that he didn't know specifics of the case.
As little as 500 micrograms of the toxin -- an amount the size of the head of a pin -- can kill an adult. Watch how ricin poisoning affects people »
Suey said seven people -- including apartment management and police officers -- had been taken to the hospital to be checked out after the ricin was discovered. None showed signs of poisoning, and all had been released, she said.
Symptoms of ricin poisoning can include anything from difficulty breathing, fever, cough, nausea and sweating to severe vomiting and dehydration.
"We did have enough ricin to be of concern," said Capt. Joe Lombardo of the Las Vegas Metropolitan Police Department.
Lombardo said areas of the hotel exposed to the toxin have been decontaminated.
The discovery of ricin alarms law-enforcement agencies because authorities in several countries have investigated links between suspect extremists and ricin.
Ricin is a poison that can be made from waste left over after processing castor beans, according to the Centers for Disease Control and Prevention.
The toxin can come in the form of a mist or pellet and can be dissolved in water or weak acid, according to the CDC. The agency also said the toxin works by getting inside the cells of a person's body and preventing the cells from making the proteins they need.
Lombardo said authorities found castor beans in the room and also powder in a small vial. He said ricin is not illegal to own, but it's illegal if processed to be used for poisoning someone.
Ricin has limited medical uses -- it can be used to kill cancer cells and bone marrow transplants.
CNN's chief medical correspondent, Dr. Sanjay Gupta, said that while a small amount can kill somebody if injected, tons of it would be needed to use as a mass terrorism tool.
Gupta said there are three ways of exposure to ricin: inhalation, ingestion or injections. If inhaled, people may develop fever, a cough, nausea, fluid in the lungs and organ failure.
There is no specific test for exposure and no antidote once exposed, he said.
There have been other reported cases involving ricin in the United States. In January 2005, the FBI arrested an Ocala, Florida, man with no known ties to terrorists or extremists after agents found ricin in the home he lives in with his mother.
Ricin was found in February 2004 in the mailroom of the Dirksen Senate Office Building in Washington. The mailroom handles correspondence addressed to U.S. lawmakers. E-mail to a friend
CNN's Kevin Bohn contributed to this report.