After a decade of painstaking research, federal and university scientists have reconstructed the 1918 influenza virus that killed 50 million people worldwide. Like the flu viruses now raising alarm bells in Asia, the 1918 virus was a bird flu that jumped directly to humans, the scientists reported. To shed light on how the virus evolved, the United States Department of Health and Human Services published the full genome of the 1918 influenza virus on the Internet in the GenBank database.

This is extremely foolish. The genome is essentially the design of a weapon of mass destruction. No responsible scientist would advocate publishing precise designs for an atomic bomb, and in two ways revealing the sequence for the flu virus is even more dangerous.

Dr. Keiji Fukuda is, by nature, composed. His voice is soft and measured. He rarely employs exclamations, never swears.

At 49, Fukuda, the top influenza epidemiologist at the Centers for Disease Control and Prevention, looks distinguished in a scruffy, academic way and reassuring. His face is unlined. His gray hair is close-cropped around his ears, making the top of his head rise like a pale dome above the timberline. He smiles often and gently. So when Keiji Fukuda admits to being as concerned as ''I have ever been,'' people who know him start really worrying.

In the past year, Fukuda has watched from his office in Atlanta as events overseas have seemed poised to spiral out of control. Between January and the end of October, 32 people have died from avian influenza in Vietnam and Thailand. Tens of millions of chickens have succumbed. Millions of others have been slaughtered. More nations have admitted to outbreaks among birds in more provinces than would have been conceivable even 18 months ago. All of this, Fukuda says, ''certainly increases the possibility'' of a much larger outbreak of avian flu among people.

Dr. Tim Uyeki, 45, one of the top epidemiologists who works with Fukuda at the C.D.C., is more excitable and blunt than his boss. ''You have the ingredients in Asia right now for a public health disaster,'' he says. Of long-term concern to him and Fukuda is that the region may be brewing a worldwide flu pandemic. ''It's a mess,'' Uyeki says. He is quiet. ''It would be nice,'' he continues, choosing his words with care, ''to be in the field, to be in Asia, to see firsthand what is going on.'' But he and the other C.D.C. scientists must be invited by other nations to help in disease investigations. Some countries prefer to do the work themselves. Others would like to keep the news of any outbreak off the world's radar screen, a difficult feat in the presence of a large international medical team.

Uyeki and Fukuda are 21st-century epidemiologists, and their job is not an easy one. They see themselves first and foremost as scientists. But in a globalized world where peripatetic germs hitch rides in the lungs or luggage of unwitting airline passengers, where sick chickens in Asia can threaten to topple third-world governments, where the role of politics and money can obscure the free flow of medical information, they cannot do their job -- preventing the spread of deadly flu viruses -- by being scientists only. They are medical monitors sitting at their desks, reading e-mail messages, Web sites, faxes and reports in order to track the varieties of flus in the United States and around the world. They are investigators who are prepared to jump on a plane to an outbreak site -- if invited -- and delicately interview the families of flu victims, trying to piece together how and why particular people fell ill and what the implications are for the rest of us. And less formally, they are diplomats, lobbyists, policy advocates, pressing for measures that governments would often prefer not to embrace.

Repeatedly invoking the threat of terrorism, the Senate on Wednesday unanimously approved a $5.6-billion, 10-year initiative to encourage private industry to develop vaccines and drugs that would protect Americans from biological, chemical or nuclear attacks.

If terrorists have access to anthrax, smallpox, botulism toxin, plague or Ebola virus, said Sen. Judd Gregg (R-N.H.), "there is no question they will use it. And they will use it in a place where people gather to go about their daily lives."

The Senate vote came more than two years after anthrax-filled letters caused five fatalities, changed the way mail was inspected and delivered, and highlighted the nation's vulnerability to bioterrorist attacks.

President Bush, who on Wednesday praised passage of the bill as "another important step in winning the war on terror," proposed Project Bioshield in his 2003 State of the Union address. The House passed a bill, 421-2, last summer, but the legislation stalled in the Senate over the technical concerns of a handful of lawmakers.

Trying to defend against self-replicating weapons of mass destruction.

Smallpox has killed a billion humans. That's more deaths than in all modern wars combined. Yet despite its virulence, smallpox typically kills only 30 percent of the population it infects. Naturally evolving pathogens keep enough victims around to kill again.

Engineered pathogens can be different - as recent work in Australia has terrifyingly demonstrated. By inserting a mail-order gene into mousepox, scientists increased the death rate in mice to 100 percent. Even after vaccination, the rate was 60 percent.

We don't know whether the mail-order gene would have the same effect with smallpox. But the very idea is an example of the fear that led Bill Joy to write his frightening piece "Why the Future Doesn't Need Us," published four years ago this month in Wired.

USC study finds meat-tolerant genes offset high cholesterol and disease.

When our human ancestors started eating meat, evolution served up a healthy bonus – the development of genes that offset high cholesterol and chronic diseases associated with a meat-rich diet, according to a new USC study.

Those ancestors also started living longer than ever before – an unexpected evolutionary twist.

The research by USC professors Caleb Finch and Craig Stanford appears in Wednesday's Quarterly Review of Biology.

The numbers astonish and horrify. According to the earliest estimates, 20 million people died during the flu pandemic of 1918. That figure is still used in classrooms and textbooks, but as John M. Barry tells us in ''The Great Influenza,'' it's certainly too low. Modern experts say that 20 million may have died in India alone, and they calculate the total number of victims at somewhere between 50 million and 100 million worldwide. No disease in human history has caused so many fatalities, not even the Black Death. The 1918 influenza pandemic killed more people in 24 weeks than AIDS has in 24 years.

The first kidney transplant, performed nearly 50 years ago, opened the possibility of replacing worn or damaged body parts. Today, with demand for replacement tissues and organs far exceeding the supply, creating new organs in the laboratory is one of medicine’s important goals.

Thanks to the development of novel biological materials and advances in stem cell biology, scientists are making functioning organs and tissues from scratch. The day when a doctor can order a ready-made kidney or bladder is still many years away, but several types of organs and tissues are now being tested in humans.

A new immunization strategy could help to prevent disease epidemics without blanket vaccination, suppress computer viruses, and even break up terrorist networks. At least, so say its designers.

All you need do is choose people at random and treat some of their friends, suggest Reuven Cohen, of Bar-Ilan University in Ramat-Gan, Israel, and his colleagues1.

"Friends just aren't normal," agrees Mark Newman, a networks specialist at the Santa Fe Institute in New Mexico. "Friends are, by definition, friendly people, and your circle will be a biased sample of the population because of it."

In a finding that may help create unlimited quantities of therapeutically valuable adult stem cells, an MIT researcher fortified adult rat liver stem cells with a metabolite that allows them to multiply like embryonic stem cells.

An injection of magnetic nanoparticles into your bloodstream could reveal precisely where harmful viruses are lurking. The particles are coated with antibodies to a particular virus, so they will form clumps that should be visible on conventional body scans if that virus is present. The team working on the technology, from the Harvard Medical School's Center for Molecular Imaging Research in Charlestown, Massachusetts, have already managed to detect viruses in body fluids and tissue samples.

Edward Jenner, the English physician who first developed the smallpox vaccine in 1796, believed that vaccination caused a fundamental change in personal constitution and would lead to lifelong immunity to smallpox. Unfortunately, this proved to be incorrect. It is now clear that immunity wanes over time. Exactly how long the vaccine confers protection, however, is difficult to assess.

Philanthropists do not typically lavish their money on swine. Or mosquitoes, for that matter.

But Bill Gates is no ordinary philanthropist. If immunizing pigs can end the spread of tapeworms, which cause virulent neurological disorders, he will pay to vaccinate them. If mosquitoes can be neutralized as malaria carriers by altering their genetic code, his money -- and lots of it -- will support the research.

"The basic science that can be applied to these problems has been advanced greatly," Mr. Gates, the chairman of Microsoft, said in a recent interview at the company's headquarters in Redmond, Wash. "So all you have to do is take a modest amount of the rich world's resources to have a huge impact on the poor world."

Get used to SARS, West Nile, Hantavirus, Ebola, Nipah, Hendra, AIDS and other new nasty infectious diseases. Health experts say we're living in a new age of infections.

And we have mostly ourselves to blame.

The nation's top scientists say that environmental, economic, social and scientific changes have helped to trigger an unprecedented explosion of more than 35 new infectious diseases that have burst upon the world in the past 30 years. The U.S. death rate from infectious disease, which dropped in the first part of the 20th century and then stabilized, is now double what it was in 1980.

The Chinese government's secrecy has been blamed for the still growing outbreak of super-pneumonia around the world that has infected over 1400 people and killed 54.