A few anthrax spores can kill, doctors say

Journal article stressing risks of low dose written by JHU biodefense expert

May 01, 2002|By Scott Shane | Scott Shane,SUN STAFF

In an assessment of scientific lessons from last fall's anthrax attacks, a panel of doctors has warned that it might take only a few microscopic anthrax spores to cause fatal disease in some especially vulnerable people.

That conclusion, published today in the Journal of the American Medical Association by experts from the Johns Hopkins University and elsewhere, stands in marked contrast to statements made by some public officials and bioterrorism experts last year suggesting that the necessary dose to cause infection was 8,000 to 10,000 spores.

That figure was the estimated number of spores required to kill half of people exposed, but it was often misunderstood as the minimum dose to cause disease.

The article's emphasis on the danger of small doses is prompted in part by the fact that no obvious source of exposure has been found for two of the five people who died.

Investigators concluded that Kathy T. Nguyen, 61, a New York City hospital worker, and Ottilie Lundgren, 94, who lived alone in Oxford, Conn., were most likely infected by spores picked up by letters passing through contaminated postal machines.

"We don't know what dose any of the victims got," said Dr. Thomas V. Inglesby, deputy director of Hopkins' Center for Civilian Biodefense Strategies and lead author of the report. "But we can assume the people in New York and Connecticut got a very low dose."

The other three fatalities were two postal workers at a Washington facility where the anthrax-laced letters were processed and a photo editor for a Florida tabloid who is believed to have opened one of the terrorist's letters.

The journal article cites a recent analysis of data on monkeys exposed to anthrax suggesting that the lethal dose for the most vulnerable 1 percent of monkeys might be just one to three spores.

The monkey experiments - carried out in the 1950s and '60s by Army scientists developing deadly biological weapons at Fort Detrick - are still the best source of hard data on the dangers of anthrax. But the experiments were initially classified, and only a small part of the data was ever published.

The article draws on a new analysis of the monkey data published in February in The Lancet by Dr. C.J. Peters, a former Detrick researchers now at the University of Texas.

"I was sort of embarrassed to write that letter to Lancet, because all the data are more than 20 years old," he said. "But no one was paying attention to it."

Peters' analysis confirms statements to The Sun last fall by Joseph V. Jemski and Edgar W. Larson, the long-retired Army scientists who performed the monkey research work, that some people might be infected by a small number of spores.

The new consensus statement on anthrax, updating one published by the same doctors in 1999, underscores the insidious nature of anthrax, whose hardy spores have proven very difficult to clear from contaminated offices and postal facilities.

Last week, Connecticut officials revealed that spores had been found in three spots on the ceiling of a Wallingford, Conn., mail processing center months after it was decontaminated.

Health officials also revealed that 3 million anthrax spores were found last fall beneath one of the mail-sorting machines at the center - all evidently deposited by cross-contaminated mail, since none of the attacker's letters is believed to have passed through the sorting center.

Three million spores is a minuscule fraction of the anthrax in each of the terrorist's letters - about one seven-hundred-thousandth of the spores in the letter to Senate Majority Leader Tom Daschle, for example. But if made airborne and inhaled, they could kill many people.

The oft-cited figure of 8,000 to 10,000 spores is an estimate, based on the monkey data, of what scientists call the LD-50 for humans - the lethal dose for 50 percent of people exposed. But susceptibility can vary widely, depending on age, underlying health conditions and genetic factors.

In the crisis atmosphere that followed the attacks, Inglesby said, "People read the LD-50 and took it as the minimum infective dose. But the floor [for infection] is far below, and it may be just a few spores."

Other important lessons from the attacks, the Hopkins researcher said, are the crucial role community doctors and nurses are likely to play in identifying any future biological attack and treating its victims. An alert physician in Florida was the first to recognize his patient had inhalation anthrax, an extremely rare disease in the United States.

Also, the experience last fall disproved the belief that inhalation anthrax is almost always fatal once symptoms appear, Inglesby noted. Six of the 11 people who contracted inhalation anthrax survived.

"Early diagnosis is possible, and it matters," Inglesby said. The consensus statement describes the symptoms and tests most useful to identify anthrax.

Among the 16 authors of the statement on anthrax are Dr. Tara O'Toole, director of the JHU biodefense center; Dr. D.A. Henderson, its founder and now the top bioterrorism preparedness official in the U.S. Department of Health and Human Services; Drs. John G. Bartlett and Trish M. Perl of the center; and experts from the Army's biodefense center at Fort Detrick and the Centers for Disease Control and Prevention.

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