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Are levels realistic in anthrax estimate?
Cleanup concerns U.S. disease expert
From Newsday, out of the
Arizona Republic, October 31, 2001
The leading American expert on the only large-scale release of anthrax powder ever recorded said Tuesday there's no safe dose for exposure, noting that some who were downwind of a 1979 accident at a Russian bioweapons plant died after inhaling as few as nine bacterial spores.
He also said his studies of the accident determined that those who were exposed were still becoming ill as long as 60 days after it occurred, demonstrating the bacteria's long incubation time.
The statements by Dr. Matthew Meselson, a Nobel Prize-winning molecular biologist at Harvard, suggests that cleanup efforts at contaminated facilities might be difficult.
They also call linto question assumptions at the heart of medical investigations under way in New York, New Jersey and Washington, D.C.
Medselson did definitive studies of the April 2, 1979, accident at the Biopreparat weapons facility in Sverdlovsk, Russia, in which hundreds of people were exposed to high-grade anthrax powder.
Meselson's 1992 study also determined that there was no threshold dose required to cause inhalation anthrax.
"There is a fair theoretical basis for saying there is no threshold," Meselson said, adding "belief in a threshold may lead you to a bad practice."
The Centers for Disease Control and Prevention in Atlanta and other health authorities have been operating under the assumption that cutaneous exposure require contact with hundreds of spores, and that an individual must inhale 8,000 to 10,000 spores in order to contract inhalational anthrax.
Based on those numbers, the CDC insists that only people who had contact with full envelope samples were at serious risk of infection.
Similarly, the New York City health department opted Tuesday to take nasal swabs only on a small sampling of health care workers at the Manhattan Eye and Ear Infirmary, the workplace of a woman, 61, who has contracted inhalational anthrax.
But Meselson said Tuesday that the idea of direct contact with the spores, and that a "blast" or high dose is required, is simply not so.
He argues that the threshold theory of anthrax exposure being used now by federal health officials is based on U.S. Army studies performed decades ago on monkeys that never reached consistent results. The range of spore doses necessary to kill half the exposed animals in those studies was from 2,000 to 50,000, varying according to how the experiments were conducted and what type of anthrax was used.
More important, Meselson said, none of the primate studies used dried powder forms of anthrax, such as have been mailed to various destinations in the United States over the past few weeks. In each monkey study, the anthrax was in a liquid suspension.
CDC Director Jeffrey Koplan was unavailable for comment about Meselson's statements late Tuesday.
But earlier in the day, Koplan said that the working assumption was that more than 8,000 spores must be inhaled to cause infection. He also noted, "Is it possible the number for humans is a smaller amount? Yes, it is."
For disease detectives and those whose job it is to ensure that a contaminated site is safe to re-enter, this uncertainty is critical.
For example, Rep. Mike Pence, R-Ind., announced Tuesday that the FBI had informed him the envelope mailed to Senate Majority Leader Tom Daschle's office that was opened on Oct.15 contained two grams of pure anthrax. If true, that represents hundreds of billions of spores, according to Meselson's calculations.
By way of comparison, the Russian incident, which sickened 88 people and killed 68, involved a total release of less than one gram of spore, dispersed over a distance of four kilometers.
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