The possibility of a worldwide pandemic of deadly avian flu has generated an alarming array of rumors, inflated fears, and false claims. Here are answers to some of the most pressing questions about the true nature of the threat and what you can do to protect yourself and your family.

The virus, called influenza A (H5N1), is unusually virulent and so new that people around the world have had no chance to develop immunity. It has killed more than half of the small number of people known to be affected so far, and the virus is running rampant among domestic flocks of chickens and other birds across an expanding range of the world, putting more and more people at risk of infection. Concerned about the tenacity of the virus, the World Health Organization expects it will take several years to stop outbreaks in domestic poultry.

Chickens and other domestic or wild birds infected with bird influenza shed the virus in their saliva, nasal secretions, and feces. Nearly all of the reported human cases have involved contact with infected birds: butchering or plucking chickens, eating undercooked poultry, or spending time in areas contaminated with the blood or droppings of birds, particularly sick or dying chickens.

At present it's extremely low. Even people exposed to sick birds seldom fall ill. While the virus has infected millions of birds worldwide, human cases remain sparse: 97 in 2005 and 116 in 2006. Reassuringly, the risk of transmission from patients to other people also has remained low. The virus has not been known to spread beyond those in close contact with a patient. What concerns public-health experts is that the evolving virus could suddenly gain the ability to spread easily from person to person, such as by swapping genes with a human flu virus. It's impossible to predict the likelihood of that happening, or how dangerous such a mutated virus would be. But given the deadly nature of the current H5N1 virus, and its uncontrolled spread among birds, health experts worldwide are trying to prepare for a possible pandemic.

No. The highly lethal strains of H5N1 influenza that arose in Asia have not appeared in any tests of wild birds or domestic flocks in North America. Related but relatively harmless strains of H5N1 virus have circulated among wild birds in the U.S. since at least 1975. These so-called "low pathogenic" strains typically cause nothing more than minor sickness in birds and pose little risk to people.

Domestic and wild cats, captive tigers and leopards, and other carnivores have contracted the virus and died after eating sick birds or coming in contact with their droppings. But infected cats have rarely transmitted the virus to other animals, and there are no known cases of such transmission to humans. So the potential role of cats in propagating bird flu appears to be small.

Your chance of contracting the H5N1 virus is currently almost nonexistent unless you've been near sick birds or have eaten undercooked poultry in regions afflicted by the virus. That said, here's how avian flu differs from seasonal flu: While both generally cause high fever and coughing, bird flu does not usually produce the runny nose, inflamed sinuses, or upper-respiratory congestion typical of seasonal flu. Instead, the sickness often advances rapidly to pneumonia, which is the most common cause of death. A rapid test for the H5N1 virus is now widely available for prompt diagnosis of bird flu.

The virus first needs to gain the ability to spread easily from person to person. The initial signs might be an outbreak among caregivers at a hospital or a cluster of cases not linked to contact with birds. Testing virus samples for significant mutations or recombination with human influenza strains could provide advance warning. In theory, health authorities should be able to contain a localized outbreak by isolating sick people and treating those who've been exposed with antiviral drugs. If that strategy fails, the virus will spread, possibly to other countries or even worldwide. At that point, attention will shift to rapid development and distribution of a vaccine, the supplying of antiflu medication to affected areas, and other broad public-health measures.

The regular flu vaccine does not prevent bird flu. Researchers have developed candidate vaccines for two variants of H5N1. The U.S. government has begun stockpiling emergency doses, and officials expect to obtain enough to treat about 8 million people by the end of 2007. Larger quantities of vaccine would probably not be widely available until several months after the start of a pandemic. That's because developers must design the final version to closely match the mutating virus before starting large-scale manufacturing. And the capacity of manufacturing plants would likely fall short of the demand for vaccine during a pandemic. So public-health authorities would probably reserve vaccines at first for high-risk groups, such as frontline health-care workers and people who've been exposed to the virus.

The pneumococcal polysaccharide vaccine, or PPV, protects against bacteria that invade the lungs of people weakened by influenza. But it's not known whether the shot would provide any protection in cases of bird flu, which can cause deadly pneumonia on its own, without any bacterial infection. The vaccine is currently recommended for people age 65 and older as well as everyone over age 2 who has diabetes, heart disease, kidney failure, or other systemic diseases that might weaken immunity or the lungs. Signs of an imminent bird-flu pandemic would probably make that step more important than ever, even if the benefit hasn't been proved. Whether other people should get the shot in that situation would be up to the individual and his or her doctor, until more definitive evidence emerges.

Animal studies suggest that two prescription drugs--oseltamivir (Tamiflu) pills and zanamivir (Relenza), an inhaled medication--may reduce the severity of the illness. Limited experience in humans suggests that starting treatment early may boost the chance of survival. However, higher doses and longer treatment may be required for bird flu than for ordinary flu. And in several patients, the H5N1 virus has developed resistance to oseltamivir. Currently circulating strains of the virus are resistant to an older class of flu drugs, including rimantadine (Flumadine) and amantadine (Symmetrel), but those still could potentially be used during a pandemic if a sensitive version of the mutating virus emerged as the dominant strain.

That's a bad idea. You should use oseltamivir and zanamivir only if your doctor confirms the diagnosis. With a private supply available at home, you or your family members could be tempted to take the medicine when it's not needed, for instance, when you just have a bad cold. That needlessly exposes you to possible side effects and, on a broader scale, it may increase resistance to the drug. Moreover, private hoarding could worsen current worldwide shortages and hamper efforts to make emergency supplies available to people who need them the most. The U.S. government has warehoused enough flu antivirals to treat 16 million people and expects to have enough for 36 million by March 2007.

Beware of pitches for formulas and supplements claiming to protect you from bird flu. The Food and Drug Administration has taken action to stop the makers of more than a dozen products from making such misleading and unsubstantiated claims. One substance heavily marketed for flu protection, colloidal silver, has no proven use against any illness, and even low doses can eventually build to toxic levels in the body. Some evidence suggests that black elderberry syrup can ease the symptoms of seasonal flu, but no one knows whether it would help with bird flu. And there's no guarantee that the syrup contains what the label says, since dietary supplements are virtually unregulated by the government.

A disposable mask that bears a label from the National Institute for Occupational Safety and Health (NIOSH) and is rated N-95 or higher and that fits tightly over your nose and mouth can prevent inhalation of virus-bearing droplets from a cough or sneeze. Packages of them are available in hardware and building-supply stores and cost about $12 to $25. In a pandemic, it would make sense to wear one in trains, buses, and other crowded places. Simple hand washing provides significant protection against flu viruses of all kinds. Using soap and warm, running water, rub your hands together vigorously for 15 to 20 seconds before eating or preparing meals and after using the bathroom or blowing your nose.

Many public-health authorities question the usefulness of aggressive quarantines. They believe that efforts to round up and confine all exposed individuals would probably be ineffective. Instead, the latest flu-pandemic guidelines from the U.S. Centers for Disease Control and Prevention recommend home or hospital isolation of people with confirmed or probable cases only. In a moderate pandemic, the CDC may recommend voluntary home quarantine, that is, urging family or other housemates of a sick person to stay home for seven days--the incubation period of the virus--after that person's symptoms appear. In a severe pandemic, the CDC could also recommend closing schools, indoor stadium events, theater performances, and other large gatherings, as well as urging businesses to allow employees to work at home. The CDC says federally imposed quarantines are likely "only in rare situations," such as at ports of entry. (For more information, go to the U.S. government's pandemic flu Web site.)

To be on the safe side, the CDC recommends you store a two-week supply of water and food, which can be useful in other types of emergencies, such as power outages and disasters. You should also keep basic health supplies on hand, including pain relievers, stomach remedies, and cold medicines.

There's no reason not to, provided you take certain precautions. Check with the Centers for Disease Control and Prevention for the latest updates on disease risks and recommendations specific to your destination. Travelers to areas with known outbreaks of H5N1 should avoid contact with chickens, ducks, and geese, live food markets, and other places likely to be contaminated with poultry or other animal excrement. And make sure your food is well cooked: Poultry should be heated until the interior is no longer pink, and eggs until the yolk is firm.

In addition to the sources cited above, here are two of the most comprehensive and reliable Web sites:

• The U.S. Centers for Disease Control and Prevention
• The World Health Organization, including an update on human cases by country.