He demonstrated by turning the device in his hands. "As it turns around, you get excellent perfusion of the tissues, and the blood vessels start to go everywhere. Then you add Ebola, and then you can do tests of drugs. I've got four of these units running in BL-4 right now." He added that he had another device in the hot lab that looked like "something out of Star Trek." He was using it to run tests on monkey blood infected with monkeypox.

Hatfill felt strongly that a bioterror event could happen one day, and he feared it could be very bad. He took me down the hall to see a bioterrorism-emergency storeroom. The room was full of racks holding boxes of safety gear and face masks and portable Racal s.p.a.ce suits. "If there's an attack on a city with a large area of coverage," he said, "one third of the population will try to flee, and so you won't be able to get into the city by road. We can stockpile emergency supplies on trains. The system we envision has twenty-seven trains, to address what to do with twenty thousand casualties. Do you know what this is?" He showed me another gadget, a big one, a kind of motor with tubes, sitting next to a biohazard stretcher. "That's a mobile embalming pump." He explained that USAMRIID's emergency planners kept one on hand for disinfecting the bodies of the victims. "Once you've got the formalin in you, you're no longer infective, and we can give you some semblance of a Judeo-Christian burial," he said.

Some of Steven Hatfill's claims about himself didn't check out: the Army said he had not served in the U.S. Special Forces. On at least one of his resumes, he had claimed to have a Ph.D. in cell biology from Rhodes University in South Africa; officials there insisted he had never been awarded a Ph.D from that inst.i.tution. He was given a secret-level national-security clearance in 1999, around the time he went to work for SAIC. Then, in 2001, he had applied for a higher-level clearance, and so he was given another background check. The government suddenly removed all of his security clearances in August of 2001, two months before the anthrax letters were mailed.

Microbiologists are naturalists, and like naturalists everywhere, they like to collect examples of interesting creatures. They can ama.s.s large and varied collections of microscopic life-forms, and often they have their own freezers and their own private labeling systems for vials. When a researcher retires, dies, or moves on, his or her freezer typically hangs around. As long as a freezer is plugged in and running, whatever is inside it will continue to exist. Once the freezer's owner is gone, the freezer can just sit there unnoticed, a mystery freezer. One day in August 2002, somebody noticed such a freezer sitting in hot suite AA5 at USAMRIID-the Ebola suite. The freezer had been used by Dr. Steven Hatfill when he worked as a postdoc there. It contained many vials and samples of pathogens with which Hatfill had been working. An FBI HMRU team put on s.p.a.ce suits, entered AA5, put evidence tape around Hatfill's freezer, and brought it out of the hot zone and transported it inside a sealed biohazard container to the CDC, where it was placed in the Maximum Containment Lab.

Aftermath of an Experiment During the anthrax event, Lisa Hensley kept her head down and worked on her smallpox data. n.o.body from the FBI called her or gave her a polygraph exam, and she felt oddly disappointed about that. She was not involved with the anthrax investigation at USAMRIID.

Meanwhile, the scientific community had begun to hear rumors that Peter Jahrling and his team had re-created smallpox in monkeys and that Jahrling had plans to write a paper about it. D. A. Henderson, who was now working inside the U.S. government, was clearly not happy about this monkey work, but he couldn't speak out in public because the official policy of the government was to develop alternatives to the traditional vaccine.

Henderson felt that a stockpile of the traditional vaccine would be more than adequate. He worked with officials from the CDC to develop a national plan for a smallpox emergency. The CDC would give ring vaccinations to the affected populations, and if those failed, everyone who could tolerate the vaccine would get it. At the same time, the U.S. Public Health Service (the parent of the CDC) would inst.i.tute quarantines around cities. The National Guard would most likely have to be involved, and so the plan had elements of martial law.

When Henderson had retired as the dean of the Johns Hopkins School of Public Health, he was replaced by an epidemiologist, Dr. Alfred Sommer, who had worked in the CDC's Epidemic Intelligence Service during the years of the Eradication. In 1970, when the cyclone hit Bhola Island, which would inspire Larry Brilliant and Wavy Gravy to go there to try to help, Al Sommer was already there. He happened to be stationed in Bangladesh with the CDC, and he ended up organizing help in an area of jungle islands in the Ganges Delta known as the Sunderbunds, not far from Bhola Island. He pioneered some of the first techniques of disaster-a.s.sessment epidemiology, methods that are now used everywhere to monitor diseases in populations that have been hit with a natural disaster.

Not long afterward, Bangladesh won its independence from Pakistan. During the civil war, ten million refugees ended up living in camps just inside India, where smallpox broke out. Sommer fought smallpox for two months in the refugee camps, often the only medical doctor at the scene. "It was just me and a couple thousand cases of smallpox, which meant five hundred to eight hundred deaths," he said.

He discovered that local cemeteries were a good place to trace the movement of the virus. "People buried their dead in Bangladesh rather than cremating them, as they do in India," he said, "and they always knew when a person died of smallpox." He studied the registries of burials, and he could see the rising and falling of the generations of the virus. He used this information to determine where to set up a ring, where to vaccinate people. Today, Sommer keeps a certificate from the WHO on the wall of his office, noting his partic.i.p.ation in the Eradication. He is as proud of it as of his Lasker Award, which is the most prestigious award in medicine. He received the Lasker for research in vitamin A deficiencies and blindness.

One day in January 2002, Sommer was having lunch at the Hamilton Street Club in Baltimore, which is frequented by journalists and literary types. An editor from the Baltimore Sun showed him a front-page article from the day before, about Peter Jahrling and his work with smallpox at the CDC, and said, "The USAMRIID people are killing monkeys with smallpox, and they're proud of it. What do you think of that, Al?"

Sommer said that his reaction was, "Excuse me? They're what?" He stared at the newspaper and couldn't believe what he was reading. "I started to vibrate at the visceral level," he said. "We could have eradicated smallpox completely if we had just destroyed the stocks a couple of years after the Eradication. And now there was Peter Jahrling exulting in the fact that he could kill these monkeys with smallpox. I went bananas." Sommer was leaving on a trip to Thailand the next morning, but he whipped off an op-ed piece for the paper.

It began: "One needn't be a Luddite to recognize an idiot-and the government scientists gloating ... over their ability to infect monkeys with smallpox are idiots of the worst sort." Sommer says that the editors wanted to tone him down, so they took out the following sentence: "I am not sure if they are homicidal idiots or suicidal idiots."

He felt that the biggest danger of Jahrling's research was that it would look suspicious to other countries and would encourage them to do their own experimentation. "We could start an arms race over smallpox, and the thinking would go, 'You could be bioengineering smallpox, so I'm going to bioengineer smallpox, as well.' I don't think it would be hard to bioengineer smallpox," he went on. "My virologist friends are always bioengineering viruses. I could see a bioengineered strain of smallpox getting into a terrorist's hands, and that's my fear. And then when we get a terrorist attack with smallpox, and the smallpox doesn't respond to the vaccine, we're in trouble." He wanted the United States and Russia to get together to destroy their stocks, jointly scour the world for stray stocks of smallpox, and use every effort to persuade other countries to destroy them. He wanted to create an international abhorrence for any nation that would keep smallpox around. He wanted the demon cast out. "It still rankles me," he said, "that we are giving smallpox to animals that could not get smallpox naturally, in order to protect humans, when the last time a human had smallpox was 1978, and humans shouldn't naturally get it today.

This is my circular indignation."

I visited D. A. Henderson at his home in Baltimore a little over two months after the anthrax attacks. I arrived in the late afternoon, bringing smoked salmon and a bottle of Linkwood malt whisky.

Nana Henderson spread out the salmon with lemon and onion on a table in the family room. Their son Doug, who is now a composer, was there. As a teenager, Doug had traveled with his father, and had vaccinated many people himself. In the cool, dry light of a winter's afternoon, the Hendersons and I poured out gla.s.ses of Linkwood and picked away at the salmon. D.A. talked about why people had joined the Eradication: "Some of them were looking for themselves, and some of them got involved with feeling what a difference you could make if you could end this disease." The sky began turning to dusk.

Pots of dead thyme sat on the deck, silvery and dry. "Smallpox was the only disease we know of for which there were deities," he said. "It was the worst human disease. I don't know of anything else that comes close."

Later, on the subject of Peter Jahrling's work infecting monkeys with variola, Henderson said he was not optimistic that it would lead to new drugs or vaccines. "Do we need to do the research? There are some scientists who feel it's important and should be pursued. But is it really going to work? Peter Jahrling gave the monkeys a huge dose of virus, but it isn't going to be very helpful for testing a new vaccine, because what we really need is an inhaled dose of smallpox in a monkey to test a vaccine, since people inhale the virus." He sounded discouraged, emotionally drained over the fight to destroy the public stocks of smallpox. He was working for the government, and government policy was to look for new cures for smallpox, and that meant doing experiments with variola. He said that he had taken care of his emotions over the issue of destroying the known stocks of smallpox. "Everything is in neutral right now,"

he said. "There is no point in my entering a battle where the cards are stacked. I'm playing along with what they're doing. I'm asking them to pursue the research." Henderson had gone so far as to suggest to Peter Jahrling that he try an African strain of smallpox, Congo 8, on the monkeys, because it might look more like human smallpox. "If it works, Peter, I want the credit," he said to Jahrling.

"When the research with variola has been pursued to some reasonable point, then I want to revisit the question of destruction," he said. "The subject should be reopened."

He had thanked me for the smoked salmon that day. "It's really large," he remarked. "I wonder: is it one of the newer genetically engineered salmon? It's fairly simple to add one gene to a salmon. Or to any organism in the lab. Will people change organisms in the lab to make them more dangerous? Can it be. done? Yeah. Will it be done? Yeah, it will be done," he said. "And there will be unexpected crises."

On April 30th, 2002, a group of six experts on the spread of infectious diseases met under conditions of secrecy in a conference room at the John E. Fogarty International Center at the National Inst.i.tutes of Health (the NIH), in Bethesda, Maryland. Each expert had been asked to create a model of the spread of smallpox in the United States, starting with a small number of infected people. One of the experts-Dr. Martin Meltzer of the CDC-found that smallpox could be easily controlled with ring vaccination using the traditional vaccine. He felt that the virus was not very infective in people and would be unlikely to spread fast or far. The other five experts disagreed with one another, sometimes sharply, but in general they found that smallpox would spread widely and rapidly. They argued forcefully with each other (as scientists do), but in the end, none of the experts could predict what smallpox would do-not to the satisfaction of the other experts. "Our general conclusion was that smallpox is a devastating biological weapon in an unimmunized human population," one of the partic.i.p.ants said. "If you look at the real-world data from a 1972 outbreak in Yugoslavia, you find that the multiplier of the virus was ten: the first infected people gave it to ten more people, on average. Basically, if you don't catch the first guy with smallpox before he kisses his wife, it goes out of control. We could be dealing with hundreds of thousands of deaths. It will absolutely shut down international trade, and it will make 9/11 look like a cakewalk. Smallpox can bring the world to its knees." The experts were told by NIH officials that they should not publicize their findings.

Last Part -- Superpox

Dr. Chen's Viruses

Unanswered questions hung over variola, and not just the question of whether ring vaccination would work if there was a terror attack with smallpox. The more troubling question was how molecular biology would affect the future of smallpox. Poxviruses are used in laboratories all over the world precisely because they are easily engineered. Commercial kits for the process are available at no great cost. It should not be forgotten that the director of the Iraqi virus-weapons program, Dr. Hazem Ali, was a pox virologist trained in England, and one a.s.sumes that he is not the only professional bioweaponeer in the world with advanced credentials in biology.

The Australian team of mouse researchers led by Ronald Jackson and Ian Ramshaw had put the IL-4 mouse gene into mousepox and had created a superpox that appeared to break through the mice's immunity. The Jackson-Ramshaw virus was harmless in people, but it seemed to be devastating in immunized mice.

Bioterror planners wondered: if the human IL-4 gene were put into smallpox, would it transform smallpox into a super variola that would devastate immunized humans? The Jackson-Ramshaw virus had been a narrow beam of light shining across a dark landscape of the future. It had shown dim outlines of virus weapons to come.

When an experiment gives a result, the first thing scientists do is try to repeat the experiment to see if they can get the same result. The essence of the scientific method lies in the repeatable result: if you perform an experiment in the same way, nature will do the same thing again. This is the heart of science and is the sign that an observable phenomenon in nature has been found. Would the results of the Jackson-Ramshaw experiment bear out? Could a poxvirus be engineered to crash through a vaccine?

One day in early 2002, I parked my car in a downtown neighborhood of St. Louis and walked along an uneven sidewalk toward the St. Louis University School of Medicine. The neighborhood is humble but neat, and is largely African-American. There are row houses with porches tucked up against the street. American flags hung from several porches or were on display in windows. The school of medicine is a stately neo-Gothic brick building, trimmed with pink midwestern sandstone, and on that day it glowed with warmth in winter light.

The facade gives way to a concrete, fortresslike structure, five stories tall, with small windows, where the research laboratories are located. In a group of rooms on the fourth floor, a pox virologist named Mark Buller leads a group of researchers who do experiments with mousepox virus and with vaccinia. They work mainly with mice-the mouse is the standard animal used in biomedical research.

Most of the important discoveries about how our immune systems work were made originally in experiments done with mice.

Mark Buller is a tall, lanky, self-effacing man in his fifties, a dual citizen of Canada and the United States, with curly black hair, a black mustache, intelligent brown eyes behind round gla.s.ses, and a voice that has an attractive Canadian softness. He grew up in Victoria, British Columbia. He often walks around the lab in nylon wind pants, a T-shirt, and running shoes. He keeps a spare jacket and tie hanging on the wall of his office, in case an important meeting comes up. Buller is known and respected among pox virologists, although he seems to deliberately avoid the limelight. "My goal in life is to be prominently in the shadows," he said to me.

Buller began hearing a lot about the Jackson-Ramshaw experiment from Peter Jahrling and Richard Moyer. Right after it was published, Moyer, especially, raised alarms-he began saying, quietly, to Buller that either he or Buller should try to repeat the experiment. The Australian smallpox expert Frank Fenner had advised Jackson and Ramshaw to publish their work, partly on the grounds that n.o.body would really make an IL-4 smallpox, since it might be too devastating and perhaps even suicidal.

In the wake of September 11th, the release of a genetically engineered smallpox into the United States did not seem quite so impossible.

Mark Buller decided to create an IL-4 mousepox, to see if it would blow through a vaccine. He wanted to get a sense of whether a human IL-4 smallpox could become a supervirus, and if so, what vaccination strategy for people would work against it. I arrived at Buller's lab as the experiment was getting under way. I wanted to hold an engineered superpox in my hands and get a feel for where the tide of modern biology was taking us.

Mark Buller leaned back at his desk, his hands clasped behind his head. His office was crowded with books and papers, and there was an exercise mat on the floor. On a whiteboard on the wall, his daughter, Meghan, had drawn a caricature of him as a science nerd, with c.o.kebottle spectacles, a brushy mustache, and a bunch of pens in his shirt pocket.

"If there is a bioterror release of smallpox, currently the main strategy is ring vaccination," he said.

"In order for ring vaccination to work, the vaccine has to block severe smallpox disease in people. But what if a smallpox that's expressing IL-4 blocks people's immune responses?"

Buller explained that his group would make four different engineered mousepox virus strains.

They would all have the IL-4 gene in them, but they would be slightly different from one another. One of them would be almost the same as the Australian engineered pox. "We want to get a feeling for what the IL-4 gene does in mousepox," Buller said. "I've always found that whenever I try to predict Mother Nature I'm wrong."

Buller's lab was a group of rooms with white floors and cluttered black counters and shelves.

Four or five people were working on different projects, and it was a crowded place. In a corner, under a window, a scientist named Nanhai Chen was in the middle of the virus engineering. He was working at a counter that was three feet long and a foot and a half wide. Virus engineering doesn't have to take up much real estate. Mousepox virus, even engineered mousepox, is harmless to humans, because the virus simply can't grow inside the human body, so the work was safe for the people in the room.

Nanhai Chen is a quiet man in his late thirties. He grew up on a collective near Shanghai called the Red Star Farm, where his father was a farmer and where some of his sisters still live. In high school, Chen decided he liked biology, and he went on to have a fast-track career at the Inst.i.tute of Virology at the Chinese Academy of Preventive Medicine in Beijing, which is probably the top virology center in China. He became an expert in the DNA of vaccinia virus. Mark Buller hired him out of China.

Nanhai Chen has a fuzzy crew cut, hands that work rapidly, wirerimmed spectacles, and restrained manners. He and his wife, Hongdong Bai, who is also a molecular biologist, have given their children American names, Kevin and Steven. He wears only two outfits, one for winter and one for summer. His winter outfit is a blue cotton sweater, blue slacks, and white running shoes. I spent days with Chen during the time he engineered the mouse supervirus. "It's not difficult to make this virus," he said to me one day. "You could learn how to do it."

A virus that has been engineered in the laboratory is called a recombinant virus. This is because its genetic material-DNA or RNA-has genes in it that come from other forms of life. These foreign genes have been inserted into the virus's genetic material through the process of recombination. The term construct is also used to describe it, because the virus is constructed of parts and pieces of genetic code-it is a designer virus, with a particular purpose.

The DNA molecule is shaped like a twisted ladder, and the rungs of the ladder-the nucleotides-can hold vast amounts of information, the code of life. A gene is a short stretch of DNA, typically about a thousand letters long, that holds the recipe for a protein or a group of related proteins.

The total a.s.semblage of an organism's genetic code-its full complement of DNA, comprising all its genes-is the organism's genome. Poxviruses have long genomes, at least for viruses. A pox genome typically holds between 150,000 and 200,000 letters of code, in a spaghettilike knot of DNA that is jammed into the dumbbell structure at the center of the pox particle. The poxvirus's genome contains about two hundred genes-that is, the pox particle has around two hundred different proteins. Some of them are locked together in the mulberry structure of the particle. Other proteins are released by the pox particle, and they confuse or undermine the immune system of the host, so that the virus can amplify itself more easily. Poxviruses specialize in releasing signaling proteins that derange control systems in the host.

For example, insect poxes release signals that cause an infected caterpillar to stop developing and grow into a bag packed with virus.

The human genome, coiled up in the chromosomes of every typical cell in the human body, consists of about three billion letters of DNA, or perhaps forty thousand active genes. (No one is certain how many active genes human DNA has in it.) The letters in the human genome would fill around ten thousand copies of Moby-d.i.c.k: a person is more complicated than a pox.

The IL-4 gene holds the recipe for a common immune-system compound called interleukin-4, a cytokine that in the right amounts normally helps a person or a mouse fight off an infection by stimulating the production of antibodies. If the gene for IL-4 is added to a poxvirus, it will cause the virus to make IL-4. It starts signaling the immune system of the host, which becomes confused and starts making more antibodies. But, paradoxically, if too many antibodies are made, another type of immunity goes down -cellular immunity. Cellular immunity is provided by numerous kinds of white blood cells. When a person dies of AIDS, it is because a key part of his or her cellular immunity (the population of CD4 cells) has been destroyed by HIV infection. The engineered mousepox seems to create a kind of instant AIDS-like immune suppression in a mouse right at the moment when the mouse needs this type of immunity the most to fight off an exploding pox infection. An engineered smallpox that triggered an AIDS-like immune suppression in people would be no joke.

To create a construct virus, you start with a cookbook and some standard ingredients. The basic raw ingredient in Chen's experiment was a vial of frozen natural wild-type mousepox virus, which sat in a freezer around the corner from his work area. The other basic ingredient was the mouse IL-4 gene.

Chen's cooking, so to speak, involved splicing the gene into the DNA of the poxvirus and then making sure the resulting construct virus worked as it was supposed to.

Chen ordered the IL-4 gene through the Internet. It cost sixty-five dollars, and it came by regular mail at Mark Buller's lab in November 2001, from the American Type Culture Collection, a nonprofit inst.i.tute in Mana.s.sas, Virginia, where strains of micro-organisms and common genes are kept in archives. The gene arrived in a small, brown gla.s.s bottle with a screw top. Inside the bottle was a pinch of tan-colored dry bacteria E. coli, bacteria that live in the human gut. The bacterial cells contained small rings of extra DNA called plasmids, and the plasmids held the IL-4 gene. The IL-4 gene is a short piece of DNA, only about four hundred letters long, and it is one of the most common genes used in medical research. To date, more than sixteen thousand scientific papers have been written on the IL-4 gene.

The standard cookbook for virus engineering is a four-volume series in ring binders with bright red covers, ent.i.tled Current Protocols in Molecular Biology, published by John Wiley and Sons.

Nanhai Chen took me to a shelf in the lab, pulled down volume three of Current Protocols, and opened it to section 4, protocol 16.15, which describes exactly how to put a gene into a poxvirus. If anyone puts the IL-4 gene into smallpox, they may well do it by the book. "This cannot be cla.s.sified," Chen said, running his finger over the recipe. "No one ever thought this could be used for making a weapon. The only difficult part of it is getting the smallpox. If somebody has smallpox, all the rest of the information for engineering it is public."

"Are you personally worried about engineered smallpox?"

"Yes, I am," he answered, holding the cookbook open as he spoke. "I was talking last week with my mentor in China. His name is Dr. Hou, and he's a very famous virologist in China. He told me the Russians have a genetically modified and weaponized smallpox. My mentor didn't say where he learned this, but I think he has good access to information, and I think it is probably true. Smallpox was all over the world thirty years ago. It could be anywhere today. It's not hard to keep back a little bit of smallpox in a freezer."

I will omit the subtleties of Chen's work for the sake of general readers, but the outline of a recipe for making the biological equivalent of an atomic bomb is in these pages. I would hesitate to publish it, except that it's already known to biologists; it just isn't known to everyone else. It doesn't take a rocket scientist to make a superpox. You do need training, though, and there is a subtle art to virus engineering. One becomes better at it with experience. Virus engineering takes skill with the hands, and in time you develop speed. Chen felt that with a little luck he could engineer any sort of typical construct poxvirus in about four weeks.

Chen took the little brown gla.s.s bottle of dry bacteria that contained the IL-4 gene and cultured the bacteria in vials. Then he added a detergent that broke up the bacteria, and he spun the material in a centrifuge.

The cell debris fell to the bottom of the tubes, but the DNA plasmid rings remained suspended and floating in the liquid. He ran this liquid through a tiny filter. The filter trapped the DNA that held the IL-4 gene. He ended up with a few drops of clear liquid.

Next, Chen spliced some short bits of DNA, known as promoters and flanking sequences into the plasmid rings. He did this basically by adding drops of liquid. Promoters signal a gene to begin making protein. The various promoters were going to cause the strains of engineered mousepox to express the IL-4 protein in differing amounts and at different times in the life cycle of the virus as it replicated in cells.

The next step was to put the engineered DNA into the virus, using a genetic-engineering kit called a transfection kit. Transfection is the introduction of foreign DNA into living cells. A transfection kit is essentially a small bottle filled with a reagent, or biochemical mix; a bottle of it costs less than two hundred dollars. You -can order transfection kits in the mail from a variety of companies. Nanhai Chen used the Lipofectamine 2000 kit from Invitrogen.

Chen grew monkey cells in a well plate, and then he infected them with natural mousepox virus.

He waited an hour, giving the virus time to attach to the cells. Then he added the IL-4 DNA, which he'd already mixed with the transfection reagent. He waited six hours. During that time, the IL-4 DNA was taken up into the monkey cells, which were also infected with natural mousepox. Somehow, the IL-4 DNA went into some of the mousepox particles, and the IL-4 gene ended up sitting in the DNA of the mousepox virus.

Chen had long days of work ahead of him, for he had to purify the virus strains. Purification of a virus is a core technique in the art of virus engineering.

A virus is a very small object, and the only way to handle it is to move around cells that are infected with it. A poxvirus growing in the layer of cells at the bottom of a well plate will kill the cells, forming dead spots in the layer. These spots are like the holes in a slice of Swiss cheese, and they are known as plaques. You can remove the dead or dying cells with a pipette. The cells that come out of that spot will contain a pure strain of the virus.

"Would you like to do some plaque picking?" Chen asked me one day. He led me into a small room behind his work area, where there were a couple of laboratory hoods, a couple of incubators (which are warming boxes that keep cell cultures alive), and, tucked away in a corner, a microscope with binocular eyepieces.

Chen put on a pair of latex gloves, opened the door of an incubator, and slid out a well plate. It had six wells, glistening with red cell-culture medium, and a carpet of living cells covered the bottom. He carried the well plate across the room and placed it on the viewing stand of the microscope. You could see with the naked eye the holes in the cell layers. The cells were infected with a strain of engineered IL-4 mousepox.

I sat down at the microscope, and Chen handed me a pipette that had a cone-shaped plastic tip with a hole in it, like a very fine straw. You put your thumb on a b.u.t.ton on the pipette, and when you pushed the b.u.t.ton you could pick up a small amount of liquid and deposit it somewhere else.

I was beginning to feel a little strange. We were handling a genetically engineered virus with nothing but rubber gloves. "You're sure it's not infective?"

"Yes, it is safe."

I sat down at the microscope and looked into a carpet of monkey cells growing at the bottom of a well. Each cell looked like a fried egg; the yolk in the cell was the nucleus. I started looking for holes in the carpet, where the virus would be growing.

"I can't find any plaques," I said. I began moving the well plate around. Suddenly, a huge hole appeared. It was an infected zone, rich with engineered virus. The cells there were dying and had clumped up into sick-looking b.a.l.l.s. The cells had caught the engineered pox.

I was holding the pipette in my right hand. I maneuvered the tip into the well plate. "I can't see the tip," I said, jabbing it around in the well.

I was wrecking Chen's careful work, but he made no comment. Then the tip of the pipette heaved into view. It looked like the mouth of a subway tunnel.

"You need to scratch the cells off," Chen said.

I moved the tip around, sc.r.a.ping it over the sick cells. I let the b.u.t.ton go, and a few cells were slurped up into the pipette. Chen handed me a vial, and I deposited a picked plaque of engineered poxvirus into it. "I don't think I'd make a good virologist."

"You are doing fine."

The work of creating four engineered mousepox strains took five months-the work was painstaking, and Chen had to check and doublecheck every step of the process. He believes that the total cost of laboratory consumables ran to about a thousand dollars for each strain. Virus engineering is cheaper than a used car, yet it may provide a nation with a weapon as intimidating as a nuclear bomb.

It was time to infect some mice with the engineered virus, to see what it would do. The mouse colony was kept in a Biosafety Level 3 room on the top floor of the medical school. Mark Buller and I put on surgical gowns, booties, hair coverings, and latex gloves. We pushed through a steel door into a small cinder-block room, where hundreds of mice were living in clear plastic boxes, set on racks behind gla.s.s doors. The mice had black fur. They were a purebred laboratory mouse known as the Black 6, which is naturally resistant to mousepox.

Buller opened some boxes, removed some mice, and placed them in a jar that had an anesthetic in it. The mice went to sleep. One at a time, he held a mouse in his hand, stuck the needle of a syringe into its foot, and injected a drop of clear liquid. The liquid contained about ten particles of engineered IL-4 mousepox-an exceedingly low dose of the virus.

Seven days later, my phone rang early in the morning. It was Mark Buller. One of the lab techs had just checked on the mice, he said, and some of them had a hunched posture, with ruffled fur at the neck. "They're going to go fast," he said.

The next morning, Buller, Chen, and I put on gloves and gowns and went into the mouse room.

There were two boxes of dead mice. Two of the strains of IL-4 mousepox had wiped out the naturally resistant mice. The death rate for those groups was one hundred percent.

Buller carried one box inside a hood and opened it. The dead mice were indeed hunched up, with ruffled fur and pinched eyes. Natural mousepox does not cause a Black 6 mouse to become visibly sick at all.

"Wow. Wow," Chen said. "They're all hunched over. This IL-4 has a really funny effect. This is really a strong virus. I'm really surprised." He hadn't expected his virus to wipe out all the mice. It disturbed him that he could make such a powerful virus, but he also felt excited.

"It's really impressive how fast this virus kills the mice at such a low dose," Buller said.

I sat on a chair before the hood, peering into it beside Buller. He reached in and lifted a dead mouse out of a box, and held the creature in his gloved hand. Without the mouse, there would be no cures for many diseases, and dead mice had been responsible for the saving of many a human life, but what he held in his hand was not a rea.s.suring thing.

Buller showed me the standard way to dissect a mouse: you slit the belly with scissors. He spread open the abdomen with the scissors, looking to see what the pox had done.

The virus had blasted the mouse's internal organs. The spleen had turned into a bloated blood sausage that was huge (for a mouse's spleen) and filled much of the mouse's belly. It was mottled with faint grayish-white spots, which Buller explained is the cla.s.sic appearance of a mouse's organs infected with pox. Doctors who opened humans who had died of hemorrhagic smallpox saw the same cloudy effect in their organs. With the tip of the scissors, he pulled out the mouse's liver. It had turned the color of sawdust, destroyed by the engineered virus. With ten particles of the construct virus in its blood, the pox-resistant mouse had never stood a chance.

There are two ways to vaccinate a mouse against mousepox. One way is to infect it with natural mousepox. When it recovers (if you vaccinate a resistant breed of mouse, it will recover), it will be immune. The other way is to vaccinate the mouse with the smallpox vaccine - that is, you infect the mouse with vaccinia, and its immunity to mousepox goes up in the same way that a human's resistance to smallpox goes up after a vaccinia infection.

Mark Buller and his group began testing IL-4 mousepox on vaccinated mice, and they got strange results. They were not able to completely duplicate the Jackson-Ramshaw experiment. They discovered that mice immunized with natural mousepox become completely imnune to IL-4 mousepox-it did not break through their immunity after all. That was very encouraging. It contradicted part of the Jackson-Ramshaw experiment. But in doing preliminary experiments with the smallpox vaccine, they had begun to see something more troubling (the experiments were in progress, and Buller wasn't able to report any real findings yet). It seemed that the IL-4 mousepox could crash through the smallpox vaccine, killing the mice if they had been vaccinated sometime previously. But if their vaccinia vaccinations were very fresh, they were protected against the engineered pox. It suggested that an engineered IL-4 smallpox might be able to break through people's immunity, but not if the vaccinations were recent, perhaps only weeks old.

Buller didn't sound as if he thought the world was coming to an end. "We showed that you could find a way to vaccinate mice successfully against the engineered mousepox," he said to me. "Even if IL-4 variola can blow through the smallpox vaccine, I feel there are drugs we can develop that will nullify the advantage a terrorist might have by using IL-4 variola. We really need an antiviral drug," he said. He argued that a drug that worked on pox was not only needed as a defense against an engineered superpox, but was also needed in order to cure people who were getting sick from the vaccine during a ma.s.s vaccination after a smallpox terror attack.

Any nation or research team that wanted to make a superpox would have to test it on vaccinated humans to see if it worked. "If you're talking about a country like Iraq," Buller said, "human experimentation with smallpox is imaginable. If you've got a guy like Saddam Hussein, and his scientists tell him they need some humans so they can check out an engineered smallpox, he'll say, 'How many do you need?' There are people like that in every age."

Nanhai Chen seemed a little less optimistic. "Because the IL-4 mousepox can evade the vaccinia vaccination, it means that IL-4 smallpox could be very dangerous," he said. "This experiment is very similar to the human situation with the smallpox vaccine. I think IL-4 smallpox is dangerous. I think it is very dangerous."