Global Health

Study: Human-to-Human Bird Flu Transmission Rare

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A new study finds that the much-feared avian flu is rarely — if ever — transmitted from human to human. But some experts don't think the question is if there will be a human-to-human avian flu epidemic, but when. Alex Chadwick talks with Dr. Paul Offit, chief of infectious diseases at Children's Hospital in Philadelphia, about the chances the virus will mutate into a form deadly to humans.


First the lead, a study published in today's issue of the magazine Nature explains why bird flu is rarely or never transferred from human to human. The disease settles deep in the lungs and we sneeze and cough from higher up so we wouldn't pass it around easily. That's good news, especially because scientists think migrating wild birds may bring the flu here in the next month or so. Dr. Paul Offit is chief of infectious diseases at Children's Hospital in Philadelphia.

Dr. Offit, welcome to the program. And this study out in Nature, this is pretty hopeful, isn't it?

Dr. PAUL OFFIT (Chief of Infectious Diseases, Children's Hospital): Yeah it's, what's not new is that you know that bird flu binds to a particular receptor and that human flu binds to another receptor. That's always been known. What's new about this is that those receptors that bind bird flu are really deep in the lung and so although people can get infected with bird flu and it can cause pneumonia, it doesn't spread from person to person because it doesn't, the virus doesn't reproduce itself, you know, in like the trachea and then the bronchi. So that, that is hopeful, you're right.

CHADWICK: And this transmission from person to person, this is the condition that's necessary for a pandemic. That is, a really wide spread of the disease in a way that would be truly terrifying.

Dr. OFFIT: Absolutely. You know, if you look at the 1957 flu pandemic which began in Hong Kong, you know, then they had a population about two and a half million, there were 250 thousand people infected within about a month. I mean it spread like wildfire through that community. So you're never going to have a pandemic until the virus spreads not only from person to person but easily from person to person. And the bird flu currently circulating in Asia doesn't do that.

CHADWICK: And what you would conclude from this study in Nature is that the disease would have to mutate in a more complicated way than we had earlier assumed. Or maybe it would have to make two mutations in order to evolve into this pandemic threat.

Dr. OFFIT: Well, I think that people always knew, researchers always knew that in order for this to become a pandemic strain, the bird virus is going to have to bind to the receptors that are in that, are in the respiratory tract, specifically in the upper respiratory tract, I think that so-called alpha two six receptor. And you know, so the question is will bird flu mutate to cause that particular binding? And I mean there are many people who believe that it will never do that. And for good reason, actually. These kinds of viruses, the H5 viruses, have been around for almost a hundred years and have never caused a pandemic.

CHADWICK: Well, so what do we conclude in sort of a public health way from this study? That is, where do public health doctors and people who are worried about bird flu go with this?

Dr. OFFIT: I think what I'd like to believe is true, is that public health doctors are worried about the next pandemic. Because there will be a pandemic. There's three pandemics every century. There's no reason to believe this century will be any different. And so preparing for a pandemic, which is to say getting what is a fairly crumbled vaccine infrastructure up and running so that we could meet, you know, tremendous needs for this country and from other countries, that's a good idea.

I idea pinning our hopes on the notion that bird flu will be that pandemic strain, I think is a little misleading. Because there are many people who believe that probably won't be the pandemic.

CHADWICK: Okay, good. Thank you, Dr. Paul Offit, Chief of Infectious Diseases at Children's Hospital in Philadelphia. Dr. Offit, I think you meant our fears, not our hopes, that this is going to be the one, correct?

Dr. OFFIT: Right.

CHADWICK: All right, Dr. Offit, thank you.

Dr. OFFIT: Okay.

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