Ricin: one drop is all it takes.

• Position: Bioterrorism - Brief article

Scientists have completed the first human clinical trial of a recombinant vaccine for the deadly toxin ricin--a potential bioterror threat--and the results indicate it is safe and effective in eliciting ricin-neutralizing antibodies, report researchers from the University of Texas Southwestern Medical Center, Dallas.

"Our major concern in this trial was safety," stresses Ellen Vitetta, director of the Cancer Immunobiology Center. "We have taken a very deadly toxin and genetically engineered it to be safe and to induce protective immunity in humans."

Ricin, which can be administered in food and water or sprayed as an aerosol, is extracted from castor beans. There currently is no approved vaccine to prevent ricin poisoning in humans, and the biological agent has a long history of use in espionage. According to the Centers for Disease Control and Prevention, Atlanta, a lethal dose of injected ricin can be as little as 500 micrograms, an amount that would fit on the head of a pin.

Depending on how the ricin is...