11 August 1999

US Agriculture Under Threat From Bioterrorism

by Kate Melville

Larry Madden, a professor of plant pathology at Ohio State University, said at a conference yesterday that experts need to begin identifying which pathogens would pose the greatest threat to American agriculture if used by bioterrorists.

"The idea is if we can know which pathogens are most likely to be used, those are the ones that regulators can look out for," he said.

Madden, a world expert on plant epidemiology, talked about what makes a pathogen a risk. Among the factors: How easily it can be produced, how well it would survive and spread in this country, the types of crops that are susceptible, and the amount and type of damage it can cause.

"These are the types of things that matter in understanding, at least in part, whether a pathogen in a crop is important enough to be concerned about," said Madden, who works at the Ohio Agricultural Research and Development Center in Wooster.

Taken together, Madden said, the factors can be used to compile a "most unwanted" list of plant pathogens. In fact, the U.S. government is working toward just such a goal. A recent workshop in Washington D.C. looked at ways to assess plant pathogens and their potential use in bioterrorist attacks. Madden and other scientists participated. A formal arrangement for assessing pathogens -- involving the Defense Intelligence Agency and the U.S. Department of Agriculture -- is in the works, Madden said.

Soybean rust is an example of a pathogen that could blast a major crop, Madden said. It's not native to the United States. It spreads fast and ruins yields.

But yield loss isn't the only threat. Some crops produce toxins when infected by certain pathogens. Even small amounts of some of these toxins can cause sickness and death in people and livestock.

An attack using one of these pathogens could lead to big problems, Madden said. An entire crop might have to be screened or destroyed, even if only a small part was infected.

"That's probably the scariest part," he said. "A problem might not be obvious at first." And because of that, a contamination -- no matter how big or small -- could cause a loss of confidence in the safety of the food supply, Madden said. That would harm farmers, consumers and business. Furthermore, the nature of these toxins might open the door to hoaxes, he said. "These (hoaxes) might be as effective as actually spreading a pathogen. If people thought that a product was contaminated, they might not buy it even if it wasn't."

He described a scenario in which a pathogen, such as the one that causes wheat stem rust, is genetically engineered to be especially virulent. It's sprayed in the air from a single small plane. The spores - millions of them - last a long time and are spread by the wind. Infections produce even more spores. If the conditions are right - and that's a big "if" - an epidemic could occur. Infection of a seed source is another possibility, and Madden said it's a greater risk than it used to be. Reason: A lot of the seeds planted in the United States are now grown in other countries, and fewer companies control this production. It's another factor to be aware of, he said.

However, whether a bioterrorist incident ever happens - and succeeds - depends on many factors. "Just because a pathogen causes a serious disease in one part of the world doesn't mean that an introduction into the United States is automatically a bad thing," Madden said. "The climate may be different. The insect vector may not be present. There are a lot of things at play that affect the spread of a pathogen."