Interview with WHO Bird Flu Expert "A Ticking Time Bomb in Your Backyard"

Avian flu has hit Asia hard, causing the deaths or destruction of hundreds of millions of chickens. Last year, 37 people also died. It's the worst such avian outbreak in centuries and experts say that its spread among humans is only a matter of time. Dr. Klaus Stohr, who coordinates the WHO global influenza program, spoke with SPIEGEL ONLINE about what the pandemic will look like, the difficulties of preparing for it and why backyard ducks are such a menace.


A February World Health Organization (WHO) report on avian influenza stated that at no time since 1968 -- when the last flu pandemic hit -- has the world been as close as we currently are to a massive outbreak. How at risk are we?

Dr. Klaus Stohr: The risk assessment is based on two observations. The first is that influenza pandemics occur three or four times every century. It has been calculated that, on average, an influenza pandemic occurs every 27.5 years. It is clear that another pandemic will happen. The second reason is based on our knowledge of how pandemics occur. We know that all deadly influenza viruses have had some traces of avian influenza virus in their genetic material. The combination of avian influenza genetic material with that of human viruses leads to a new virus that has characteristics of both -- namely the high transmissibility of human flu combined with the deadliness of avian flu. Basically, the question is not if it will happen, but when.

SPIEGEL: So in other words, the fact that hundreds of millions of chickens have died in Asia is a warning signal that an outbreak among humans is imminent?

Stohr: Yes. The avian influenza virus currently infecting Asia's poultry is more widespread than any that has been seen in the last centuries. It has now been seen in 10 countries and has proven impossible to eradicate. Our best guess is that the virus will be around in Asia for at least the next three to five years. As soon as it infects a person who is already ill with the human flu, the unhappy marriage between the two viruses will result in the break out of a pandemic. As long as this avian virus sticks around, we are at very high risk of a pandemic.

SPIEGEL: How dangerous will this pandemic be?

Stohr: Influenza pandemics are a little bit like earthquakes. We know that they are going to happen but we don't know exactly when or how strong they are going to be. The pandemics in 1957 and 1968 were relatively mild with between 1 to 4 million dying in each. That is cause for concern, but compared to the really bad pandemic of 1918, where at least 40 million and perhaps more than 50 million people died, it is a small number. Taking into account the increase in the world population since then, one would estimate that a mild pandemic would result in between 2 to 7 million deaths and a further 28 million hospitalized. Health care systems will be overwhelmed very quickly.

SPIEGEL: That sounds like a best case scenario. Some have predicted that between 50 and 100 million might end up dying from the coming pandemic. What would the worst case look like?

Stohr: Anything is possible. We have relatively little data from the pandemics that preceded 1918 and that one may have been an exception. The situation I just outlined -- which is very likely -- is enough cause for concern.

SPIEGEL: Why do we need to be worried about flu pandemics at all? Healthcare has vastly improved since 1918. At that time the first influenza virus hadn't even been isolated yet. Aren't all these warnings of a coming pandemic just fear-mongering?

Stohr: The world since 1918 has indeed become better able to combat influenza pandemics. But only part of the world. Don't forget that two-thirds of the world's population live in developing countries in Asia and the annual per-capita spending for healthcare in the region is very low. In Vietnam, for example, it's just $3. That's not much different from Europe in 1918 and perhaps even less. The majority of the world population is still very vulnerable. Global transportation has also improved dramatically, which helps viruses spread more quickly. It took six to eight months for the 1957 virus to spread around the world. With SARS in 2003, a virus which was much less transmissible than a flu virus, it traveled from Asia to Canada and Europe within just a couple of weeks.

SPIEGEL: Flu viruses are constantly mutating. How can you prepare for a pandemic when you don't even know what to expect?

Stohr: Pandemic preparation is damage control and nobody will be 100 percent prepared. Once this virus is out of the box, its global spread cannot be prevented. But preparation will necessarily vary from country to country. The United Kingdom, for example, has just signed a contract to stockpile enough antivirus medicine for 25 percent of its population. Australia, France, Canada and the United States have likewise started purchasing medicine. But the UK commitment will cost them €290 million. That is 10 times more than Vietnam's entire annual health budget and they have over 80 million inhabitants. Thus, it is clear that the anti-viruses that are being developed will only be available in very small numbers for very rich countries.

SPIEGEL: Why do such pandemics tend to start in Asia?

Stohr: Influenza viruses need to spread from animals to humans before they can cause a pandemic and two thirds of the world's population lives in Asia as do an overwhelming number of domesticated animals and poultry. So the sheer concentration of susceptible hosts is certainly one of the reasons. Another reason is the proximity between animals and humans. In Asia there are 220 million households which have a backyard farm. That's different than in Europe where animals are often kept in large industrial farms and people don't generally keep a couple of ducks in their backyard.

SPIEGEL: The February avian influenza report also mentioned that scientists are worried because the virus is becoming "stealthier." What does that mean?

Stohr: The avian virus in Asia is a very serious disease. Close to 100 percent of all the chickens infected with it end up dying. And when they die it's not too difficult to see that there is something wrong -- it's a clear warning signal. But now, this highly deadly avian virus has moved into the duck population, which I didn't think could ever happen. The tricky thing is that 40 percent of the infected ducks have no clinical signs of infection; protecting yourself from a healthy, quacking duck is much more difficult than from a dead chicken lying on its back on the ground. Because ducks excrete just as much deadly virus as a mortally ill chicken, they become a ticking time bomb in your backyard. You can no longer see the virus.

SPIEGEL: What does the situation look like right now?

Stohr: So far this year, there have been almost twice as many human cases in Vietnam than at the same time last year despite the fact that only half of the provinces that had outbreaks last year are infected. This could mean that our surveillance has improved. But the infections are no longer originating on the large farms -- where controls have improved -- but rather from somewhere else. There have also been fresh outbreaks among poultry in Indonesia, Vietnam and Thailand.

SPIEGEL: So we still need to be worried about this virus?

As long as this virus is in Asia, you should be worried. It's like if you own a car and you know that one of the tires is going to rupture because you have seen a weak spot. You may drive more safely because of the danger, but before you have replaced the tire, you know it can blow. And that is the situation with this influenza virus in Asia.

Interview conducted by Charles Hawley

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