They've confronted incidents in Michigan and Ontario, faced activity on the south border and are tracking a potential threat to a DoD computer system, he said. At the same time, they're monitoring a suspicious incident in the northeastern United States that's affected utility and energy supplies. Kucharek declined to share too many specifics that might tip off exercise participants to what's coming or interfere with its realism.

"We're feeling every bit of it," Kucharek said of the exercise, affirming the promise Navy Adm. Timothy J. Keating, NORTHCOM commander, made last week of a "very aggressive" Ardent Sentry scenario.

"It is not an open-book test," Keating told reporters during a May 4 media day at NORTHCOM's Peterson Air Force Base, Colo., headquarters. "It will be very challenging for us, and that's the point."

Just as in real-life crises, NORTHCOM is playing a supporting role to first responders during the exercise, as spelled out in the National Response Plan. "We're not the lead," Kucharek said. "We may only be monitoring, or we may send support as requested."

No large-scale troop movements are planned, but military units involved will conduct field training at Selfridge Air National Guard Base, Mich.; Tyndall Air Force Base, Fla.; and an abandoned mining town in Playas, N.M., now owned by the Department of Homeland Security, he said.

While testing the military's interagency coordination, the exercise also focuses on its ability to operate with the Canadian government and the newly established Canada Command, NORTHCOM's Canadian counterpart, Kucharek said.

"This is the first major exercise which will allow Canada Command to train with federal and provincial departments and agencies," said Gordon O'Connor, Canada's national defense minister. "Exercises such as Ardent Sentry 2006 help ensure we respond to domestic threats and natural disasters in a coordinated manner." It also will promote "cross-border information sharing" between Canada Command and NORTHCOM, he said.

Ardent Sentry builds on lessons learned during Hurricane Katrina, which Keating called NORTHCOM's "first real acid test" since its establishment in October 2002 to provide command and control of DoD homeland defense efforts and to coordinate military assistance to civil authorities.

"We learned a lot, and we observed much," Keating told reporters last week. "We're working really hard to take lessons observed and make sure they are lessons learned and mistakes not repeated."

New procedures introduced since Katrina will reduce NORTHCOM's response time and improve communications and damage assessment, he said. They'll reduce the time it takes to get assets where they're needed and help tailor the type of assistance provided to the specific need.

In addition, a new cell phone tower will improve communications among first responders, particularly in areas where existing communication lines are down.

Keating said he's confident NORTHCOM is prepared to face whatever natural or manmade disaster it faces, including the hurricane season that begins June 1.

"I can't imagine anything else we could do or should do," he told reporters last week. "We are fully operational, we are as ready as we can be for this upcoming hurricane season, as well as our response to any other natural or manmade disaster."

New vaccines and medications generally undergo three test phases of increasing scope to see whether they work and have any side effects.

The trial vaccine is administered in two doses and requires a booster shot.

Thirty-one vaccines against bird flu are currently being tested on humans, 22 of them against the H5N1 strain. Eight vaccines will have undergone Phase II trials by the year's end.

The big fear is that the H5N1 virus, which at present circulates among poultry, could acquire genes that could make it highly contagious among humans.

As this has not yet happened, the present prototype vaccines are configured on the avian strain that, according to an official World Health Organisation (WHO) toll dating from May 8, has killed 115 humans through transmission from birds.

The hope is that these vaccines, if stockpiled, may provide some protection against a pandemic strain and help brake an outbreak. They could also be swiftly adjusted to cope with the pandemic strain once it is identified, it is hoped.

In a commentary also carried out by The Lancet, two US flu experts, Suryaprakash Sambhara and Gregory Poland, cautioned that no-one knows for sure whether the pre-pandemic vaccines will provide any shield.

And, they noted, the Sanofi Pasteur vaccine has a drawback because it is a two-dose formula. This limits the number of doses that can be stockpiled because of the constraints on global manufacturing capacity.

In thousands of samples collected in Africa this winter, the bird flu virus, A(H5N1), was not detected in a single wild bird, health officials and scientists said. In Europe, only a few cases have been detected in wild birds since April 1, at the height of the migration north.

The number of cases in Europe has fallen off so steeply compared with February, when dozens of new cases were found daily, that specialists contend that the northward spring migration played no role. The flu was found in one grebe in Denmark on April 28 - the last case discovered - and a falcon in Germany and a few swans in France, said the World Organization for Animal Health, based in Paris.

In response to the good news, agriculture officials in many European countries are lifting restrictions intended to protect valuable poultry from infected wild birds.

Last week, the Netherlands and Switzerland rescinded mandates that poultry be kept indoors. Austria has loosened similar regulations, and France is considering doing so. The cases in Europe in February were attributed to infected wild birds that traveled west to avoid severe cold in Russia and Central Asia but apparently never carried the virus to Africa. The international scientists who had issued the earlier warnings are perplexed, unsure if their precautions - like intensive surveillance and eliminating contact between poultry and wild birds - helped defuse a time bomb or if nature simply granted a reprieve.

"Is it like Y2K, where also nothing happened?" asked Juan Lubroth, a senior veterinary official at the United Nations Food and Agriculture Organization in Rome, referring to the expected computer failures that did not materialize as 1999 turned to 2000. "Perhaps it is because it was not as bad as we feared, or perhaps it is because people took the right measures."

Still, he and others say, the lack of wild bird cases in Europe only underscores how little is understood about the virus. And scientists warn that it could return to Europe.

"Maybe we will be lucky and this virus will just die out in the wild," Mr. Lubroth said. "But maybe it will come back strong next year. We just don't have the answers."

The feared A(H5N1) bird flu virus does not now spread among humans, although scientists are worried it may acquire that ability through natural processes, setting off a worldwide pandemic. The less bird flu is present in nature and domestically on farms, the less likely it is for such an evolution to occur, they say.

Worldwide, bird flu has killed about 200 humans, almost all of whom were in extremely close contact with sick birds.

Specialists from Wetlands International, who were deputized by the Food and Agriculture Organization, sampled 7,500 African wild birds last winter in a search for the disease. They found no A(H5N1), Mr. Hagemeijer said, so it is not surprising that it did not return to Europe with the spring migration.

While bird flu has become a huge problem in poultry on farms in a few African countries, including Egypt, Nigeria and Sudan, specialists increasingly suspect that it was introduced in those countries through imported infected poultry and poultry products. Mr. Hagemeijer said the strength of the virus among wild birds possibly weakened as the southward migration season progressed, a trait he said was common in less dangerous bird flu viruses. That probably limited its spread in Africa, he said.

A(H5N1) is the most deadly of a large family of bird flu viruses, most of which produce only minor illness in birds.

Many bird flu viruses are picked up by migratory birds in their nesting places in northern lakes during the summer and fall breeding season. As the months pass, the viruses show a decreasing pattern of spread and contamination.

"So it tends to be mostly a north-to-south spread, and then it wanes," Mr. Hagemeijer said.

Still, this means that the cycle could start again this summer, if the virus - which can live for long periods in water - has persisted in those breeding areas. Many bird specialists contend that a small number of wetland lakes in Central Asia and Russia may harbor the virus all the time, serving as the origin of European and Central Asian infections.

Scientists still do not know which birds carry the virus silently and which die from it quickly, or how it typically spreads from wild bird to wild bird, or between wild birds and poultry.

Farm-based outbreaks of bird flu still occur constantly in a number of countries, although not in Europe. Ivory Coast had its first outbreak of bird flu, on a farm, last week.

But other countries, like Turkey, have made substantial progress in containing the disease among poultry, Mr. Lubroth said. He added that he hoped that quick measures to limit outbreaks had reduced the virus's spread in Africa.

After the virus was found on farms in Nigeria in January, many specialists expected it to spread rapidly among farms and into wild birds in the region. Apparently, it did not.

"Why didn't it sweep up the coast from Niger, to Benin and Senegal and back up through Europe? Why didn't it hit Africa's big lakes?" Mr. Lubroth asked.

"All we have are a few snapshots of the virus. What we need is a movie of its life cycle."

It is causing infections from abscesses to deadly blood poisoning, bone infections and pneumonia, often in the young and the fit, including professional football players, high school athletes and previously healthy children.

Whether it spread from the hospital into the community or developed as a separate strain outside the hospital is a mystery, says John McGowan, professor of epidemiology at Emory University. But recent genome studies suggest the MRSA strain circulating in the community is significantly different from the strains that are typically found in hospitals.

"There are differences in the sequence of the community strain that may make it more virulent, more able to affect people with (healthy immune systems), and with biological differences that make it spread readily," he says.

MRSA has become so common that in many hospitals more than half of all staph infections tested are drug-resistant. That's changing the way doctors treat these common infections.

"When a patient comes in with a staph infection, we assume it's resistant until proven otherwise," says pediatrician Sheldon Kaplan of Texas Children's Hospital in Houston, where MRSA rates have gone from 33% of all staph tested in 2000 to 75%.

Drug-resistant bugs, including MRSA and several others that are emerging in hospitals, are more difficult to treat, requiring stronger antibiotics that are more costly and in some cases have to be given intravenously.

Few new drugs on the way

Few major pharmaceutical companies have new medicines in the pipeline that target the drug-resistant organisms, says George Talbot of the Infectious Diseases Society of America's task force on anti-microbial availability.

"In a number of these companies, there were active decisions taken that antibiotic research was not going to be profitable enough to meet their obligation to shareholders," says Talbot, an infectious-disease specialist and consultant to drug companies. "So they decided to go for drugs that would be taken for a lifetime - drugs for diabetes or high blood pressure - rather than drugs to be taken for a week."

Jumping into the breach are smaller biotech companies that are doing the basic research to identify promising new drugs, he says, "but it's not clear yet that these smaller companies will have the development expertise or financial wherewithal to bring them to market."

In some cases, small companies form partnerships with larger, wealthier drug companies that underwrite the costs of large-scale studies and marketing, he says, "but those deals have to be done in areas where the larger companies perceive an economic benefit."

MRSA, for instance, offers a large market because it is affecting so many people and several antibiotics can be used against it. For lesser-known drug-resistant germs, the treatment options are fewer.

MRSA has been known in hospitals since the 1970s, but in recent years, new strains, which doctors call community-acquired MRSA, have infected people outside health care settings. One of these strains, known as USA300, was identified in 2000 and has been found in at least 21 states.

"What we're seeing is the emergence of a new epidemic strain of the MRSA in the community," says Daniel Jernigan, medical epidemiologist at the Centers for Disease Control and Prevention (CDC).

The CDC has reported on the new community strain since 2000, and it reported in March that the strain had caused outbreaks in hospital nurseries in Chicago and Los Angeles. Nine of the 22 infected babies required hospitalization. Other studies have reported longer hospital stays and higher death rates in MRSA-infected patients.

Staph aureus is the most common cause of the estimated 12 million skin infections each year in the USA, Jernigan says. A study in 2003 found that about one-third of people carry staph in their noses and just under 1% of people carry MRSA. Most carry the bacteria without becoming ill.

"We think the number of people carrying MRSA is increasing," Jernigan says, but the new studies are not yet completed.

It's not certain how common MRSA infections are. A CDC study based on hospital discharge data estimates that in 1999-2000, nearly 126,000 people were hospitalized each year for MRSA infections, a rate of nearly 4 per 1,000 hospital discharges.

Another study of 11 emergency rooms across the country found that almost 60% of skin abscesses tested were caused by MRSA, Jernigan says.

The new super-strain of MRSA has been concentrated in geographic regions, including California, Texas and Georgia, but Kaplan says that is changing. "It's in Pittsburgh, Memphis, St. Louis, Omaha. It's becoming more common on the East Coast now. It's literally all over the country."

University of California researchers who sequenced the genome of USA300 reported in the March 4 issue of The Lancet that the strain contains genes that make it hardy and able to cause "unusually invasive disease" such as severe blood infections and necrotizing pneumonia, in which lung tissue is destroyed.

Community-acquired MRSA has sidelined athletes, including players with the Washington Redskins, St. Louis Rams and San Francisco 49ers, as well as dozens of high school and college football players, wrestlers and basketball players. It has broken out in prisons, military bases and day care centers, anywhere there is crowding, poor hygiene and broken skin.

You don't have to be in a gym or a jail to be at risk. "You just have to be living," Kaplan says.

"This is not a superbug from a locker room; it's just out in the community," Kaplan says. "We've got 1,700 kids coming into our hospital with staph infections. They're not playing football. They're babies. Why this has been happening over the last 10 years vs. 20 years ago, we don't know."

Barriers breaking down

Strains of MRSA that have been known in hospitals for decades still account for most of the cases. Until a few years ago, says CDC epidemiologist John Jernigan (no relation to Daniel Jernigan), "MRSA was almost exclusively associated with hospitals." The types in the community are genetically different from those found in hospitals, he says, but that line is blurring.

"There used to be this very sharp distinction. However, we have the sense that more and more those strains associated with the community are finding their way into the hospital and causing health care-associated infections."

MRSA spreads through skin-to-skin contact and can be passed by using shared objects, such as razors or towels. It frequently hits more than one person in a family, and researchers in Canada have found that pets and their human owners can pass it back and forth.

"We're seeing transmission of MRSA from people to pets and pets to people," says researcher Scott Weese of the Ontario Veterinary College at the University of Guelph. "It raises the question: Can animals be a reservoir and play a role in this ping-ponging in households?"

He says dogs, cats, rabbits and ferrets have been found carrying the USA300 strain. As in people, it can cause serious skin infections and other illnesses.

"It shows pets are mimicking what's going on in the human situation," Weese says. "We're seeing more transmission in households than in the past."

Until their son was diagnosed, Bryce's parents had never heard of MRSA.

"Never heard of it, never even thought a little bacteria could do something like this," says Scott Smith, who owns a machine shop near their home in Santee, Calif., outside San Diego.

It's unclear how Bryce caught the bug, but his parents believe he may have picked it up while they were out Christmas shopping.

The family's ordeal started with a simple cold. Bryce was having sniffles a couple of days before Christmas, but on Christmas night, his parents saw he was breathing rapidly, and they worried that he might have asthma.

They called their pediatrician, who saw them two days later, dismissed the ailment as a simple viral infection and told the parents, "I've seen this a million times."

But as the days passed, the baby's condition worsened. The parents called the doctor two more times. "He said, 'You guys are new parents,' " and he told them not to worry so much.

Finally, in the early hours of New Year's Day, "we looked at him, and I said, 'I'm afraid if I go to sleep he won't be alive in the morning,' " Smith says. "We rushed him to the hospital."

At Children's Hospital of San Diego, "it was almost like a movie script," he says. A nurse tested Bryce's blood oxygen level, and "within 30 seconds they had 10 people on him."

'Just eating away' at him

Doctors said the infection had solidified in Bryce's right lung, and surgery was needed right away to clear the lung. "They had five chest tubes in him, because the infection was not only inside the lungs but outside the lungs and just eating away at his chest."

For 12 days, the Smiths didn't know whether Bryce would make it.

Then he was put on a breathing machine. He was put into a drug-induced coma and given intravenous vancomycin, a drug that is known as the last line of defense against MRSA.

The drug is "like fire going through the veins," Smith says. "With Bryce, at that point they had him asleep, and he was asleep for six weeks, so I feel lucky that he didn't have to feel the pain of vancomycin."

Today, Bryce is almost back to normal, but Smith says he and his wife won't let anyone touch him without washing their hands first.

"I felt so guilty," he says. "What keeps going through my mind is that as my son laid there at the house, we were literally watching him die and we didn't know."

The authority and its supporters insist the change doesn't open the door to wholesale genetic testing in Britain.

"It is not going to be offered for some trivial things such as eye colour, hair colour," said Paul Serhal, a fertility expert at University College London.

In the Cohn family, cancer was a like a genetic time bomb exploding in succeeding generations. Ovarian cancer killed Betsy, then her daughter Ester. The gene was passed to Pat, another breast cancer survivor.

The risk of cancer was so great that Pat's daughter, Karen, had a double mastectomy, and next year her ovaries will be removed.

"I've got a four-year-old and I want to see her grow up," said Karen Cohn. "I felt I had no choice because the odds were stacked against me."

Her daughter, Sophie, carries the cancer gene and has a 50-50 chance of developing it. Embryo screening would ensure the gene isn't passed on.

Pushing the boundaries?

But critics such as Dr. David King of Human Genetics Alert fear the boundaries of what's acceptable are being pushed back regularly.

"I do see it as a continual pressure towards liberalization," said King. "Really a consumer-driven eugenics in which parents will be allowed complete carte blanche to choose the minutest characteristics of their children, which I do think will be disastrous for society."

His fears are shared by Emma Kearns, a breast cancer survivor. Kearns said she's glad her mother wasn't screened.

Given advances in cancer treatment, "things can kind of turn around, and you can live with cancer, and in many cases, people can get better," said Kearns.

Canada, like several other countries, permits pre-implantation genetic diagnosis for inherited diseases.

Unlike Britain, there is no national authority in Canada to oversee the practice or set boundaries.