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MONDAY, Jan. 30 (HealthDay News) -- The first human tests of a vaccine to prevent ricin poisoning show the vaccine is safe and effective, researchers at the University of Texas Southwestern Medical Center report.
Ricin is a lethal poison that is considered a potential bioterror threat. It is made from the waste left over from processing castor beans and can come in the form of a powder, a mist, a pellet or dissolved in water or weak acid.
Depending on how the ricin is given, victims develop fever, nausea and abdominal pain or lung damage, and die within a few days of exposure. There is no antidote after the first few hours of exposure, and because symptoms do not appear until later and often mimic other illnesses, people often do not know they have been exposed until it is too late for treatment.
Because castor beans are readily available, with more than 50,000 tons of castor bean extract existing around the world as a byproduct of castor oil production, public health officials warn that ricin could be used by terrorists.
There have been several incidents in recent years involving ricin in the United States and Europe. The U.S. Centers for Disease Control and Prevention classifies ricin as a "Category B" biological agent, which means it is "relatively easy to disseminate."
On Feb. 3, 2004, three U.S. Senate office buildings were closed after ricin was found in the mailroom of Senate Majority Leader Bill Frist's office. There were no injuries reported.
Now researchers have successfully tested a vaccine that could prevent ricin poisoning. The main user of the vaccine would be the military, researchers say.
Their report appears in this week's online edition of the Proceedings of the National Academy of Sciences.
"A vaccine that we developed against ricin is safe and elicited antibodies in human volunteers," said lead researcher Ellen Vitetta, director of the Cancer Immunobiology Center. "It's a small pilot study with only 15 people, but it was designed to establish those two things."
In the pilot study, three groups of five volunteers each received a series of three injections of various doses of the vaccine, called RiVax. Those who received the highest vaccine dose produced ricin-neutralizing antibodies in their blood, indicating their immune systems had responded, the researchers found.
To see whether the antibodies would prevent ricin poisoning, Vitetta's team tested the human antibodies in mice that were also injected with active ricin, and the mice survived.
"It looks like the feasibility is there to develop a large scale preparation of the vaccine, primarily for the armed forces," Vitetta said. "The actual development is going to be dependent on a number of factors."
Among those factors are the need to develop a large stockpile of the vaccine to test on many people, Vitetta said.
In addition, the researchers need to find the best way to store the vaccine to keep it stable, and to test it against the various ways ricin can be delivered. "We need to determine whether the vaccine will protect against ricin aerosol, ricin given orally or in water or food," she said.
One expert thinks that developing a successful vaccine against ricin is important to thwart a potential bioterror attack.
"These results are very encouraging," said Dr. Christopher P. Holstege, director of the Blue Ridge Poison Center in the division of medical toxicology at the University of Virginia.
Holstege believes the vaccine needs to be tested in larger groups to prove its effectiveness. "Are they going to find that there are no major adverse reactions to the vaccine?" he asked.
There is a pressing need for an effective vaccine for ricin poisoning, Holstege added. "Ricin is a bioterrorism agent that is very potent," he said. "This is something that is a risk to the general public, and to the military."
SOURCES: Ellen Vitetta, Ph.D., director, Cancer Immunobiology Center, University of Texas Southwestern, Dallas; Christopher P. Holstege, M.D., associate professor, emergency medicine and pediatrics, and director, Blue Ridge Poison Center, division of medical toxicology, University of Virginia, Charlottesville; Jan. 30-Feb. 3, 2006, Proceedings of the National Academy of Sciences online
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