Bird flu, which is not uncommon among chickens and other fowl, has the attention of global health authorities as it has spread in Asia.

Why are scientists concerned about bird flu?

A: The bird flu virus could evolve into a form that is easily spread between people, resulting in a highly contagious and lethal disease.

Q: How could this happen?

A: Someone already infected with the human flu virus might catch the bird flu. The two viruses could recombine inside the victim's body, producing a hybrid that could readily spread from person to person.

Q: Why would that be so bad?

A: The resulting virus would likely be something humans have never been exposed to before. With no immune defenses, the infection could cause devastating illness, such as occurred in the 1918-19 Spanish flu pandemic (search), which killed an estimated 40 million to 50 million worldwide.

Q: How do people catch bird flu?

A: So far in this outbreak, human cases have been blamed on direct contact with infected chickens and their droppings.

Q: How is this outbreak of bird flu different from earlier ones?

A: This outbreak has spread more rapidly into more countries, increasing its exposure to more people in many locations. An outbreak in 1997 in Hong Kong was the first time that bird flu had spread to people, but it was much more quickly contained. Also, this outbreak has now killed seven people; six died in the Hong Kong episode.

Q: How can bird flu be stopped?

A: The chief strategy is to kill infected poultry.

Q: Is there a vaccine?

A: No. One is being developed, but it will probably take many months and may not be ready in time to stop a widespread human outbreak, if one occurs.

Q: What about drugs?

A: Flu drugs exist that may be used to both prevent people from catching bird flu and to treat those who have it. The virus appears to be resistant to two older generic flu drugs, amantadine (search) and rimantadine (search). However, the newer flu drugs Tamiflu (search) and Relenza (search) are expected to work. Supplies could run out quickly if an outbreak occurs.

Q: Can people who catch the virus from birds pass it to others?

A: Yes, that was seen during the 1997 outbreak, but the disease was milder in those who caught it from infected people rather than birds.

Q: Is there more than one kind of bird flu?

A: Yes, at least 15 subtypes exist. The current one is called H5N1.

Q: How common is bird flu?

A: The disease occurs worldwide, but only the H5N1 strain has been shown to be deadly in people. Wild ducks carry flu but often do not get sick from it. All birds are susceptible to the infection. However, chickens and other domestic poultry are especially prone to rapidly fatal epidemics of the virus.

Q: Is bird flu the same as SARS?

A: No, although their symptoms are similar, SARS is caused by completely different viruses. Flu is also more contagious and cannot be as readily contained as SARS through isolating people who have the infection.