Ricin forensics: Comparisons to microbial forensics

Ricin from the castor bean plant (Ricinus communis) is the most commonly used biological terror agent in the world. The plants are common and the seeds are easy to procure. The protein toxin is extremely potent, relatively simple to extract and disseminate and there is no known antidote. Forensic investigations are similar to those used in microbial toxins where the toxin must be identified and its activity verified, and DNA from the toxin source must be present to be genotyped. Ricin however provides unique genetic challenges because the toxin sample typically provides only trace amounts of mixed DNA from a large number of plants. Furthermore, plants from around the world appear to have only a limited number of sources and are highly similar to one another genetically. Forensics must therefore rely on relatively large numbers of genetic markers to connect samples from a criminal act to those from the purported source.