MELISSA BLOCK, host:

This is ALL THINGS CONSIDERED from NPR News. I'm Melissa Block.

ROBERT SIEGEL, host:

And I'm Robert Siegel.

Earlier this week, we asked you to send us your questions about bird flu. We received hundreds from around the world, and we're going to try to answer some of them now.

BLOCK: First, though, we want to lay out some of the basic facts that we know about the virus. There are many types of influenza. The type that has health officials worried is called H5N1. It mostly affects birds. An estimated 150 million of them have either died of the disease or been killed in an attempt to stop its spread.

SIEGEL: The first human case of H5N1 occurred in Hong Kong in 1997; 18 people were infected and six died. Since then more than 100 people have been infected, and more than half of them have died. All of the human deaths have occurred in Asia.

BLOCK: In recent weeks, there have been reports of bird flu being identified in dead birds in Europe, including western Turkey and Russia, Greece and Romania. EU foreign ministers this week declared bird flu a global threat. For the record, there have been no reported cases of H5N1 bird flu in birds or humans in the United States. The fear among health officials is that the virus could mutate into a strain that can be passed easily and directly between humans.

SIEGEL: Tomorrow on the program, we'll be focusing on your questions about what the US government is doing about avian flu and what you can do if an outbreak occurs here. But today, we brought in Dr. Hon Ip, who is a virologist with the US Geological Survey's National Wildlife Health Center and who's going to answer some of your questions about the virus itself and how it spreads. He joins us from Madison, Wisconsin.

And, Dr. Ip, welcome to the program.

Dr. HON IP (Virologist, National Wildlife Health Center, US Geological Survey): Thank you.

SIEGEL: First, Joyce Kuzmin in Boston writes: `Is the media exaggerating the potential danger of bird flu?'

Dr. IP: I think that there has been a lot of press in the media, and I think the issue is very important. It certainly is important to poultry, it is very important to wild birds and it certainly is of human concern. So I think some level of media coverage is appropriate.

BLOCK: Here's another question. This one's from Len Anderson in Sylvania, Ohio, and he asks: `What's the probability of an individual US resident contracting the avian flu at this point compared to other events, such as being struck by lightning?'

Dr. IP: Ooh, that's a good question. As of right now, as we said, there is no evidence of the bird flu being in North America; not in people, not in poultry and not in wildlife. In the United States, on average, something like 82 people die per year from lightning. So since H5N1 is not yet in this country, I would say that the possibility of a US citizen dying from lightning is much higher than dying from H5N1, at the moment.

SIEGEL: Well, let's go now to a question that we got in our voice-mail box.

(Soundbite of voice-mail recording)

KRIS(ph): Hello. My name is Kris. I live in Putnam County, New York. I'm wondering what is the vector of transmission from bird to human? Do you have to be in contact with bird feces? Do you have to be in contact with the bird blood products? How is it transmitted from the bird to a human being?

SIEGEL: Hon Ip, what do we know?

Dr. IP: Contact with bird feces, yes, that is definitely a way where people could become infected. I think that it's really sort of like extended, prolonged contact with poultry if they're struggling, where they're going to be flapping their feathers, causing dander and other material. That is probably the root of infection.

BLOCK: Here's another question that has to do with birds, and this one comes from Bob Spaziano in Raleigh, North Carolina. He writes: `Is it possible for migrating birds to carry the virus to North America, or is exposure here more likely from people returning to North America from other parts of the world that have the virus?'

Dr. IP: The short answer is both. It is possible for migratory birds to carry the virus to North America. The other part of the question was international travel, and we know that international travel was a major way that the SARS virus--which also originated from this part of the world--spread rapidly around the world. And so I would say that both migratory birds and potential international traffic are ways that the virus could come to this country.

BLOCK: Hon Ip, based on what we know about the migratory paths of birds, does that lead you in any particular direction of where this virus might spread?

Dr. IP: We had initially anticipated that the virus would spread from Southeast Asia up along the Asian continent over towards Siberia and possibly contact migratory birds in North America over in the region of Russian Siberia and Alaska. But since the summer, it looks like the virus has spread, really, towards Central Asia and now into Romania and Turkey. What this indicates to us is that maybe the virus is spreading along a different route, that it's spreading towards the Black Sea and the Mediterranean flyway.

Now where it is is actually not in contact with some of the migratory birds that go from North America over into Europe, and there's a handful of species that does so. And we do not think that those birds are going to be in contact with the current migratory birds in the Black Sea at the moment, but that is one of the possible ways that it may come. So potentially from the West Coast, potentially from the East Coast.

SIEGEL: OK. Hon Ip, here's a question from Claudia Sandburg Larson(ph) in Sacramento, California. She asks: `Can humans get bird flu by eating the meat of infected birds?'

Dr. IP: Not if they thoroughly cook it first. The flu virus is readily killed by temperatures when the meat is thoroughly cooked, and thoroughly cooked means about 160, 170 degrees Fahrenheit.

BLOCK: Hon Ip, we got a lot of letters from pet owners, and here's one of them. Lisa Branson in Torrance, California, writes: `Does owning a caged pet bird increase the possibility of passing or catching the avian flu virus?'

Dr. IP: I don't think so. Having a pet bird that's inside all the time, I don't think that's a risk. It is illegal in the US to import pet birds from regions that are infected with bird flu, so likelihood of getting a pet bird that is already infected with bird flu is relatively low.

SIEGEL: Here's another pet question. Phil Travers in San Antonio, Texas, writes: `Let's say my dogs pick up a dead bird, a bird that died from avian flu. Are my dogs at risk?'

Dr. IP: What we know today is that there's no reputable report of H5N1 being in any dogs around the world. The virus has surprised us at every turn, and so I wouldn't say that it is impossible. But at the moment, I do not think that if a dog picked up a bird infected with bird flu that the dog would be likely to come down with bird flu.

BLOCK: We've got a question from a listener who gave her name just as Sarah(ph). She lives in Denver, Colorado, and she asks: `What mutation of the virus would have to happen for it to change to person-to-person, and what factors would cause that mutation?'

Dr. IP: That's a question that a lot of virologists are trying to answer. And what we're trying to do is compare the genetic sequences of H5N1 with other known human pathogenic viruses. What we know, for example, are there are mutations on the human glutinin; that's the H in H5N1. Mutations in there can allow the virus to bind better, for example, to cells in the human respiratory tract. There are also mutations in a gene called PB2 that seems to be important for the infections into humans, and there are a number of other ones like that, as well.

BLOCK: I suppose one corollary to that would be how quickly might that mutation happen.

Dr. IP: That's a very difficult question to answer. There's a number of ways which the virus can mutate. It can mutate gradually over time, or it can recombine in a co-infection. And when recombination happens, that can introduce a lot of mutation very rapidly.

SIEGEL: Wouldn't we assume that this virus would be potentially mutating in infinitely different ways in different instances?

Dr. IP: That is quite correct. I think that the virus is mutating randomly, and it is only when a particular mutation is advantageous for it to infect a particular new host, then that mutation becomes selected and it takes over.

SIEGEL: Let's go to another voice-mail.

(Soundbite of voice-mail recording)

Ms. AUDRA BASSETT(ph): Hello. My name is Audra Bassett. I live in Robbinsville, North Carolina. And my question is: How big of a threat is this to healthy adults?

Dr. IP: According to the World Health Organization, what we know about the situation in Asia is that healthy adults are being infected. In fact, the average age of those infected in Vietnam seems to be around--between the ages of 17 and 31.

SIEGEL: But those might be the ages of people who just handle chickens in terms of their work, say, or who has the job of plucking the chickens.

Dr. IP: That is quite true. It could be from the occupational exposure, or it could be from a particular predilection of the virus. And I don't think that there is enough cases for us to know that at the moment.

SIEGEL: Let's say that this mutates into a person-to-person virus. Does that mean that that form of the virus would only be spread by interpersonal contact, or might it then be transmitted back into the avian population and be further spread by birds?

Dr. IP: I think that with most flu viruses that are spread, that are human flu viruses, they're spread almost primarily as respiratory from person to person. And for the most part, there's not as much of a chance of introduction back into the wild birds once the virus becomes a human virus.

BLOCK: Hon, if this virus has been around, as we mentioned, in humans since 1997, why would there be so much more attention and seemingly so many more fears about a possible pandemic now than there were before?

Dr. IP: I think it's because that the--everybody now understands that the situation is growing. It is starting to appear in countries outside of Southeast Asia. And I think the implications of possible spread is much larger now than before.

SIEGEL: Is there a global standard of reporting here? That is, if there were cases breaking out anywhere in rural China or North Korea, for that matter, would we know about it, or are there blank spots where the epidemiology may not be telling us enough?

Dr. IP: I think that that varies dramatically from country to country. Some countries are much more restrictive in terms of where the sources of information can come from. And there's a number of reasons for doing so, one of which is to, like, make sure that a preliminary report doesn't get blown all out of scale before the confirmation comes in. Some countries report very rapidly, and we appreciate that. To me, transparency is always a good thing.

SIEGEL: But do you have the impression that today everybody's on board, everyone recognizes this threat, or are there still countries where you could do with a lot more transparency?

Dr. IP: I think that as a scientist that's involved in this evolving field, the more information, the better. So there's always room for improvement.

SIEGEL: Well, Dr. Hon Ip, thank you very much for talking with us today.

Dr. IP: You're welcome.

SIEGEL: Dr. Hon Ip, a virologist with the USGS National Wildlife Health Center, joined us from Madison, Wisconsin.

BLOCK: We obviously got a lot more letters than we could answer here, and you can get some more answers to more of those questions about bird flu at our Web site, npr.org.

And tomorrow on the program, we'll focus on your questions about how the government would respond to an outbreak and what you can do to help keep yourself and your family safe.

SIEGEL: Here are some other stories we're following on the program. The Pentagon says it's investigating claims that American soldiers desecrated the corpses of two Taliban fighters. The allegations were made in an Australian television news report. A video apparently shows two soldiers burning the bodies and taunting other fighters using loudspeakers.

Hurricane Wilma is turning towards Mexico's Yucatan Peninsula. It's now a Category 4 storm, and expected to hit land early tomorrow morning.

And the House of Representatives has passed a bill giving the gun industry immunity from most liability lawsuits. The Senate has already passed it, so it now goes to President Bush for his signature.

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