Bird Flu: "This thing just continues to march"

The CP interview: Dr. Michael Osterholm of the University of Minnesota's Center for Infectious Disease Research and Policy talks about the flu bug that could bring the world to its knees

What makes them so similar is that they both cause this cytokine storm phenomenon.

CP: Which essentially results in a person's drowning in his or her own blood as it fills the lungs, right?

Osterholm: It's even worse than that. You get that kind of leakage, yes, but it also goes in and begins to shut down all your vital organs. It's a domino effect. Your kidneys go down, then your liver goes down, you have all this destruction through necrosis of your lungs and your internal organs. Everything goes.

CP: In the limited human sample we've seen so far, this influenza has exacted a much higher mortality rate than the 1918 flu. Are there mechanisms that tend to dilute the virulence of a strain as it spreads?

Osterholm: That's a really critical question. We can only anticipate that this will attenuate. Meaning that once it starts spreading in humans, it will lose some of its punch in order to better adapt to humans. That's traditional with virtually all agents you see like this. The thing that is very difficult to talk about is, we don't know how much. If this were to go human-to-human—we talk about a worst-case scenario in terms of what happened in 1918, when roughly 2.5 percent of the world's population died. Of those who contracted it, roughly 5 to 6 percent of populations died, varying by age.

The mortality rate so far for this virus is around 55 percent, so this virus would have to attenuate a lot to get down to that level. And we do have good data. There are not a lot of mild, asymptomatic infections out there [with H5N1]. We're now aware of six studies involving over 5,000 close contacts of H5N1-infected people, in Indonesia, Vietnam, and Hong Kong, in which less than one person per thousand contacts had evidence of an H5N1 infection that was missed—that is, a mild infection.

This [virus] is not causing a lot of asymptomatic infections right now. Some people are saying there's a lot of mild [H5N1-related] illness all over out there, but it's just not true. That means we're not artificially inflating the mortality rate by missing a lot of infections. I'm actually pretty confident that the real mortality is almost that high.

So for that number to drop all the way down to a couple percent is a pretty big drop. Which says to me that when people talk about 1918 as a worst-case scenario, well, maybe that isn't the worst-case scenario. That's hard for people to hear, because then they think you're really trying to scare the hell out of people. But you know what? It's just the data.

If this virus were to ultimately go human-to-human, none of us know what the human mortality would be.

CP: Does the fact that it seems to be gaining more currency in other mammal species augur one way or the other for its becoming transmissible from person to person?

Osterholm: None of us know. In 1918, for instance, we don't know whether it infected cats and dogs. We've been trying to find that out. Nobody's got that data. There just weren't good reports. It surely can't be good that it's adapting to more species. It says that the lung receptors of chickens aren't the only ones that will take this virus. And we know humans surely will take it, on the off chance that they're exposed [to infected birds].

The bird-to-cat thing is not new. Some people have made a lot out of the German situation. That's not new. The Bengal tigers at the Bangkok Zoo died two years ago. They got fed H5N1-infected chickens, and 50 of the Bengal tigers died. They also transmitted to each other—there were cats there that did not eat the chickens. Even Albert Osterhaus's work of the past couple of weeks, which has been really important to confirm it, was not a surprise.

CP: I wanted to ask you about a scenario you described in your New England Journal of Medicine article from last year, "Preparing for the Next Pandemic." If a flu strain transmitted from human to human did break through in some part of the world, how would you expect events to unfold over the first weeks?

Osterholm: Well, look at what's already happening with the bird situation. You've got countries like South Korea saying, don't go to Egypt. You've got a lot of bird embargoes already taking place. If you saw this morning's Wall Street Journal, the travel industry in Europe is tanking. And this is a non-threat to a vast majority of humans. What we're concerned about is that if this takes off in a given area, it's going to move around the world quickly, just like SARS. Last year 750 million people crossed a national border somewhere in the world, either by plane, automobile, or on foot.

These things move fast. With SARS, we had one physician from China who came to Hong Kong, stayed in the Metropole Hotel on one floor where there were nine other individuals he infected just through breathing the air. They then took it to four different continents in the next two days. That gives you kind of a model, though influenza is much, much more infectious.

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