Their efforts join those of scientists racing to make better vaccines and treatments against diseases from anthrax to botulism -- caused by microbes that might be used in such an attack.
Other groups are working to make better detectors. The tactical advantage of using germs in warfare is that people would not even know they had been infected until they became ill -- often days or weeks later -- and it is hard to tell whether a plain white powder is harmful or a hoax.
Experts have been warning for years that the United States is unprepared for an attack, and bodies from Congress to the World Health Organization have conducted studies that suggest hundreds of thousands of people could die in a single attack.
The threat became real last week when 63-year-old Robert Stevens, a photo editor working in Florida, died from an infection he got after inhaling anthrax. Two co-workers carried anthrax spores but were treated with antibiotics before they could become ill.
Investigators are fairly sure the infection was deliberate -- perhaps a criminal attack -- and not a natural occurrence. The spores could have been delivered in something as low-tech as an envelope.
On Friday, an employee of NBC in New York was diagnosed with an anthrax infection of the skin and the Federal Bureau of Investigation said it was checking whether she was exposed after opening a piece of mail containing anthrax spores.
Infections from inhaled anthrax usually kill victims by the time symptoms surface, so workers in the Florida building are being tested for exposure and given antibiotics just in case.
One way to protect people from a possible biological attack is with vaccines, but there is a shortage of vaccines for the most probable germ agents.
For instance, there are only between 7 million and 20 million doses of smallpox vaccine -- the U.S. Centers for Disease Control and Prevention does not have precise figures.
Dr. Carol Tacket of the University of Maryland Medical Center in Baltimore was given the task this week of seeing if those freeze-dried doses can be stretched further.
Her group will vaccinate some volunteers with vaccine diluted with five times the normal amount of diluent solution, some with 10 times dilution, and a few with normal concentrations.
Over a 2½-month period beginning next month, researchers at St. Louis, the University of Maryland, the University of Rochester and Baylor College of Medicine will study 684 adults under the age of 32 who have never been vaccinated for smallpox. They will see if the diluted vaccines trigger production of protective antibodies and create a telltale scab.
"The idea is that if the vaccine will cause a 'take' when diluted, that will increase the number of doses that are stockpiled," Tacket said in telephone interview.
The need for protection against the disease, which has been eradicated in its natural form, has become more pressing since the Sept. 11 terrorist attacks. There is no treatment for smallpox, and routine vaccinations ceased in the United States in 1972 because it was no longer considered a threat. Most people vaccinated before then have lost their resistance to the virus.
Some experts fear that smallpox manufactured by the Soviet Union in the 1980s for biowarfare may have been obtained by rogue nations and could be used in bioterrorist attacks.
Tacket said people who were vaccinated against smallpox years ago may no longer be immune. But the vaccine works quickly, so perhaps it could be used even after someone was exposed. "We hope that would give us a short window of opportunity in which vaccine could be administered," she said.
"It's a very quick way to markedly expand the amount of vaccine that we already have, which on face value in the undiluted form would not be a lot. It's prudent to be prepared," said Dr. Anthony S. Fauci, head of the National Institute of Allergy and Infectious Disease, which is funding the experiment.
If the approach works, Fauci said the diluted vaccine could be ready by the end of this year.
However, diluting the vaccine is not meant to be an alternative to the new doses in production, said Dr. Sharon Frey, the lead researcher on the smallpox study at St. Louis University. "This is a stopgap measure to make more doses available until that new vaccine is developed."
The current anthrax vaccine takes much longer to take effect, and requires several boosters. But a team at the University of Texas is working to help people who have an anthrax infection too far along to be treated by antibiotics.
Brent Iverson and colleagues are working with antibodies that will quickly recognize and attach themselves to the toxin, thus inactivating it.
Iverson said his team hoped to announce progress within about six weeks. "If we can repeat and hopefully verify the results that have gotten us excited we are going to submit them for publication," he said in a telephone interview.
Steve Kornguth, who directs the University of Texas' Biological and Chemical Countermeasures Program, said the antibodies might be used to treat anthrax victims. He said the antibodies might also be the active ingredient in chip-sized anthrax detectors, being developed by another team at the university.
Commercial firms are working with government money, too.
San Diego-based Nanogen Inc. and Needham, Massachusetts-based AVANT Immunotherapeutics Inc. announced vaccine contracts this week. BioReliance, based in Rockville, Maryland, has been gearing up for months to make smallpox vaccine for the government.
Privately owned EluSys Therapeutics, Inc. makes monoclonal antibodies -- artificial antibodies made to home in on one specific target -- and is working with the U.S. military to make a reatment for anthrax, as well.
Smallpox is a viral disease that causes high fevers, rashes and sores that cover the whole body. The disease is fatal in about a third of all cases.
While inhaled anthrax is much more lethal, killing roughly 90 percent of all patients, it isn't contagious. Smallpox released in a bioterror attack, however, could spread rapidly throughout a population and infect thousands because it is passed through the air.
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