Get some dried disease agents, put them in an envelope, mail them to your victim, sit back and wait. It seems like the perfect, untraceable crime. The spores of B. anthracis are odorless and completely invisible to the human eye. Yet, left untreated in the human respiratory system, anthrax infection can lead to death within a week.
Tackling these cases has been a humbling experience for San Francisco's own Robert Mueller, who in July was appointed director of the FBI. Faced with only meager clues, including a pattern of attack and a few envelopes and scraps of handwriting, Mueller has turned to the public for help in uncovering new leads.
That's not to say these unseen killers are free to strike again with impunity, however. Quite the contrary. Though law enforcement faces a dead end in its search for suspects, a nationwide team of doctors, chemists, microbiologists and forensic scientists is hot on the trail of the anthrax bacillus itself.
Invisible Evidence
The irony is that while the human criminals remain anonymous, the unseen microorganisms that were the cause of these deaths have left behind more fingerprints than any human assassins. It's on this trail of microscopic clues that determined investigators remain focused, in hopes that even if it doesn't lead to the culprits themselves, it may yet allow us to stop B. anthracis from killing again.
For health-care workers, the first clue that something was out of the ordinary was the appearance of inhalation-form anthrax itself. Fully 95 percent of anthrax cases worldwide are of the cutaneous variety, transmitted through cuts in the skin. Only 18 cases of the inhalation form of the disease have been recorded in the U.S. throughout the 20th century, so the coincidence of two almost simultaneous infections was enough to set doctors' warning bells buzzing.
That buzz became a full-scale alarm when these cases were linked to tainted letters sent through the mail. The revelation of criminal intent also suggested another clue: Might this have been so-called weapons-grade anthrax?
To invade the human body in quantities sufficient to cause infection, particles of a dried preparation of anthrax must be sufficiently small to drift freely through the atmosphere. Commonplace spores, those greater than five microns in size, don't stay airborne long enough to be reliable as a weapon. The hallmark of a weaponized anthrax preparation is its artificially small particles.
Once such minuscule particles were discovered among powder found in the suspect envelopes, microbiologists began working to unravel still further clues. Even with weapons-grade anthrax, there's small, and then there's small. Determining just how well produced the particles actually were could help pinpoint their source, and the key to that is the fluidizing agent.
The Process of Elimination
During the manufacturing process, weaponized anthrax spores tend, like socks in the dryer, to pick up an electrostatic charge. That charge makes the dry particles clump together, weighing them down and diminishing their effectiveness. The addition of a chemical fluidizing agent negates the charge, keeping the spores small enough to remain aloft.
Before its biological-weapons program was dismantled in 1969, the United States used silica as the fluidizing agent in its anthrax experiments, blending it with the bacteria in a sophisticated process few other nations could match. One more accessible method involves bentonite, a fairly common type of clay that has a variety of industrial applications, including use as a drying agent in kitty litter. Preparing anthrax with bentonite requires grinding the dried preparation, producing larger particles, compared to other, chemical methods.
Even so, the process isn't easy. In the past, individuals in the U.S. who have attempted to manufacture weaponized anthrax have been unsuccessful, as in the case of two men arrested in Las Vegas in 1998 after boasting of their misguided experiments with a harmless form of the bacillus. The Japanese Aum Shinrikyo cult similarly failed to produce an effective bioweapon, eventually settling on sarin gas for its 1994 terrorist attack in the Tokyo subway system.
Though 50-100 facilities in the U.S. might be able to produce viable weapons-grade anthrax — and there's no telling how many covert laboratories may have been set up for that explicit purpose — it seems more likely it would be obtained from a foreign source with the will, facilities and financial backing to do the job right. Recent reports of anthrax attacks in Pakistan would seem to corroborate an overseas source; yet the question of the bacteria's actual origin remains unanswered.
Chemical Countermeasures
That's troubling for the FBI and other law-enforcement agencies, which still seem no closer to locating a suspect. The enemy of any murder investigation is often the implacable clock: Can the puzzle be unlocked before the killer strikes again? But fortunately again, thanks to contemporary technology — the anthrax mystery need not necessarily carry such a time constraint.
Though the anthrax bacillus is deadly to humans and animals, among the microbial world it's as vulnerable as any other bug. It responds to many of the same germicides as other bacteria, including a variety of modern sterilization compounds. Scientists have even begun experimenting with fumigation using chlorine-dioxide gas, a powerful antimicrobial agent that can reach into the nooks and crannies of complex environments — like office buildings — and yet leave no toxic residue.
The mail, too, can be protected. Recently, the U.S. Postal Service awarded a $40 million contract to San Diego-based Titan Corp. for electronic pasteurization equipment, which can blast letters and packages with sufficient quantities of radiation to kill any bacteria or spores contained inside. Not only will postal workers be protected, but so will the recipients of any further spore-containing packages.
The next clues scientists hope to find will be on an even smaller scale than before, all the way down to the molecular level. DNA "fingerprinting" has already identified traces of anthrax found in Florida, New York and Washington, DC, as belonging to identical strains of the bacillus. A similar technique is now being built into new biodetector equipment, which can potentially recognize disease agents in the environment before they strike another victim.
The Genetic Riddle
Taking it one step further, a $200,000 grant has been awarded to the Rockville, MD-based Institute for Genomic Research to sequence the complete genome of the anthrax specimens. One goal of this project is to determine whether the bacteria have been genetically engineered to be resistant to antibiotics — a dead giveaway that they had their origin in the weapons program of a technologically sophisticated nation, not some secret basement laboratory.
An even more important goal of DNA sequencing, however, is the advancement of medical science. Ironically, these terrorism-related cases have given doctors an unprecedented opportunity to study this dangerous organism. New combination antibiotic therapies have already proven even more effective than expected, saving the lives of patients who ordinarily might have succumbed. A better genetic understanding of the disease itself will, hopefully, lead to even more effective new treatments or vaccines.
The ultimate question, of course, still remains: Who is responsible? One frustrating aspect of the anthrax crisis is that no matter how many new ways to destroy or imprison bacteria are revealed through the progress of science, no justice will have been served. That can only come through law enforcement's ongoing efforts to find the perpetrators and bring them to trial.
In the meantime, the nation waits, while the scientific sleuths continue their search for answers. As we wonder where the next terror attack will strike, we're reminded yet again that we can never truly eliminate evil from the world. Still, you can take some small comfort in this: We may yet eliminate the threat of B. anthracis.
