A human pandemic caused by A(H5N1) is by no means inevitable. Many researchers doubt it will ever happen. The virus does not infect people easily, and those who do contract it almost never spread it to other humans. Bird flu is what the name implies: mostly an avian disease. It has infected tens of millions of birds but fewer than 200 people have contracted it, and nearly all of them caught it from birds.
However, when A(H5N1) gets into people it can be deadly. It has killed more than half its known human victims – an extraordinarily high rate. Equally alarming is that many who died were healthy, not the frail or sickly types of patients usually thought to be at risk of death from influenza.
The apparent lethality of A(H5N1), combined with its inexorable spread, are what have made scientists take it seriously. Concern also heightened with the recent discovery that the 1918 flu pandemic was apparently caused by a bird flu that jumped directly into humans.
In addition, A(H5N1) belongs to a group of influenza viruses known as Type A, which are the only ones to have caused pandemics. All those viruses were originally bird flus. And given the timing of the past pandemics – 1918, 1957, 1968 – some researchers think the world is overdue for another. It could be any Type A, but right now A(H5N1) is the most obvious.
The virus lacks just one trait that could turn it into a pandemic: transmissibility, the ability to spread easily from person to person. If the virus acquires that ability, a pandemic could erupt.
Everything hangs on transmissibility. But it is impossible to predict whether A(H5N1) will become contagious among people. The virus has been changing genetically, and researchers fear that changes could make it more transmissible, or that A(H5N1) could mix with a human flu virus in a person, swap genetic material and come out contagious.
But most bird flu viruses do not jump species to people. Some experts say that since A(H5N1) has been around for at least 10 years and the shift has not occurred, it is unlikely to happen. Others refuse to take that bet.
Q: How will we know if the avian flu turns into a pandemic that is passed from person to person?
A: If there is a pandemic, it would be everywhere, not in just one city or one country. To detect such an event as early as possible, there is an international surveillance system, involving more than 150 countries, which searches for signs that a new flu strain is taking hold in humans.
Q: When people die from avian flu contracted from birds, what kills them?
A: Like victims of severe pneumonia, many patients die because their lungs give out. The disease usually starts with a fever, fatigue, headache and aches and pains, like a typical case of the flu, but within a few days can turn into pneumonia and the patients' lungs are damaged and fill with fluid.
In a few cases, children infected with A(H5N1) died of encephalitis, because the virus attacked the brain. A number of people have also had severe diarrhoea – not usually a flu symptom – meaning that this virus may attack the intestines as well. Studies in cats suggest that in mammals the virus attacks other organs, too, including the heart, liver and adrenal glands.
But more detailed information about deaths in people is not available because very few autopsies have been done.
Q: If I got bird flu, how would I know?
A: There is no reason to suspect the disease unless you may have been exposed to it. The early stages of the illness in people are the same as those of ordinary flu: fever, headache, fatigue, aches and pains. But within a few days, people with bird flu often start getting worse instead of better; difficulty breathing is what takes many to the hospital. In any case, patients with flu-like symptoms that turn severe or involve breathing trouble are in urgent need of medical care.
Q: If I'm sick, can I be tested for avian flu?
A: There is no rapid test for bird flu.
Q: Do any medicines treat or prevent bird flu?
A: Two prescription drugs, Tamiflu and Relenza, may reduce the severity of the disease if they are taken within a day or two after the symptoms begin.
Q: If there is an epidemic of flu in humans, how can I protect myself?
A: If there is a vaccine available, that would be the best option. But if there is no vaccine, it may be hard to avoid being infected. Flu pandemics spread quickly, even to isolated regions. The 1918 flu reached remote Alaskan villages where the only way visitors could arrive was by dog sled.
Q: If bird flu reaches my country, will it be safe to eat poultry or to be around birds? What about pigs, ducks and other animals?
A: Poultry is safe to eat when it is cooked thoroughly, meaning that the meat is no longer pink and has reached a temperature of 82 degrees Celsius. The risk is not from cooked meat -- cooking kills viruses. Instead, it is from infected birds that are still alive or have recently died. So the person who killed an infected chicken, butchered it or put it in the pot would be at greater risk than the one who ate it.
© The New York Times