Potent anthrax not stuff of amateurs

Richard Butler

(CNN) -- Anthrax isn't necessarily hard to obtain or reproduce, but turning it into a potent weapon requires a degree of sophistication, experts say.

In addition to a variety of natural strains across the globe, there are genetically modified strains that may be more resistant to antibiotics.

But whatever the strain, the most potent anthrax must be finely ground to the right size.

"If the particles are too small they would be inhaled and exhaled without being retained in the lungs. If they are too large, they would just fall on the ground because you couldn't inhale them," a federal law enforcement official said.

The optimum size is believed to be about 5 microns or slightly less, said experts. A micron is one-millionth of a meter.

"That kind of powder, of course, can be easily carried up in the air," said Stanford University bioterrorism expert Steven Block. "It forms an aerosol. It tends to lead to the worst forms of anthrax, like inhalation anthrax, but it's not easy to make."

Simple anthrax can be grown in a fermenter, almost like home-brewed beer, explained Richard Butler, former chief weapons inspector for the United Nations.

But producing potent or so-called "weaponized" anthrax, which must be dried and milled with the right machinery, isn't the work of amateurs, officials said

"I think Iraq spent millions of dollars in getting that machinery, and you need know-how," Butler said.