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Coming to grips with bird flu

NBC News’ Ned Colt sat down with Dr. Scott F. Dowell, director of the CDC's "International Emerging Infections Program" last week in Bangkok to discuss the dangers posed by the bird flu outbreak.
Vietnamese workers clean chickens at a privatley run slaughter house for chickens on the outskirts of Ho Chi Minh City, Vietnam, on Feb. 25.Richard Vogel Stf / AP file
/ Source: NBC News

Late last month a regional director of the World Health Organization warned that the WHO believes "that there is now the greatest possible danger of a pandemic," caused by the spread of Avian Influenza, also known as bird flu.

Millions of birds have died or been culled in Southeast Asia in the past year, as bird flu has become endemic to the region. It's now found not only in birds, but in pigs, cats, and even humans. At least 45 people have died in the past year of bird flu in Thailand and Vietnam.

NBC News’ Ned Colt recently sat down with Dr. Scott F. Dowell, Director of the CDC's "International Emerging Infections Program" to discuss the outbreak. The Bangkok-based program is a collaboration between the CDC, and the Thai Ministry of Health. The following are excerpts from that interview.

Ned Colt: Where do we stand regionally in terms of bird flu and its impact on humans at this point?
Dr. Scott F. Dowell: It continues to be a significant concern, we're still seeing outbreaks of the H5 virus among poultry in Thailand, and we're reading about outbreaks in neighboring countries, so the problem in the poultry population seems to be endemic.

What does that say about long-term impact?
I think we have to be cautious about saying that a pandemic is going to happen or predicting when it will happen, because one thing about influenza viruses is they're very hard to predict, and this could go on for some time without a pandemic.

It's fair to say though that it's a continuing concern, and that the longer this virus is present in the poultry population, with occasional introductions into the human population, the more we have concerns about a pandemic.

Why is it that this virus could find it easier to survive in the longer term, and to move into human hosts?
The great concern is the virus will acquire the ability for transmitting from person to person, and that's going to happen in one of two ways.

Either there's a re-assortment event, where the human virus re-assorts with the avian virus:  they exchange gene fragments, and you get a new virus with the virulence of the chicken flu, and the transmissibility of the human flu. Or, through a gradual series of mutations the avian H5 acquires the ability to transmit from person to person.

And how typical is that evolution in the world of flu viruses?
Influenza viruses evolve, that's what they do. They mutate with every replication and they change over time. And we have already seen the H5 virus mutating and changing over time. Since it was first seen in Hong Kong in 1997, the properties of the current virus are different from the 1997 virus. That will continue to happen.

And does that then make it much more dangerous, much more virulent to humans?
I don't know if that's necessarily the case. It may be more or less dangerous to humans. What we've seen since 1997 is not encouraging however. If you look at the mortality in 1997 in Hong Kong it was about 33 percent. The mortality currently in Vietnam and Thailand has held steady at about 70 or 75 percent. So there are certainly signs that are not encouraging about the direction that this virus is evolving.

"Not encouraging"... That sounds fairly scary, that seven out of ten people who contract it will likely die from it.
Certainly, this virus right now is one of the deadliest viruses that affect humans. The good thing is that it doesn't affect very many, so far. It's a rare event that the virus is passed from poultry into humans, and when that has happened — it's even rarer that it's passed from human to human. So, so far we don't have an efficiently transmitted virus, although it's a very lethal one.

Is there any way then to control this? In such a huge region?
No, I think there's a recognition now that this is an endemic problem in this part of the world, and we probably need to move from efforts to try and eradicate the virus altogether in small groups of intensive culling operations, to figuring out how to control the level of the virus over the longer term.

Where does avian flu stand in the pantheon of deadly viruses?
For me in the emerging infections field, an influenza pandemic is the big concern. If we look over the last one hundred years at the impact of emerging infections on humans, the 1918 pandemic dwarfs everything else. And so this current concern with the H5N1 virus certainly needs to be elevated to the top of our list of concerns about emerging infections in 2005.

And that again is because it has the potential to be so virulent?
Right. The 75 percent fatality rate of avian influenza puts that virus at the very top of the list of the most lethal pathogens that affect humans. It's right up there with rabies and Ebola and Marburg virus. We assume, and we hope, that if it acquires the ability to transmit from person to person, that the mortality will be considerably lower than that, but it's guesswork about how much lower.

So the big worry is that it will become an "efficiently transmitted virus.” How do you stop that from happening?
That's what we're watching for. The less virus there is in the poultry population, the less likelihood there is that that is going to change, and mutate into an efficiently transmitted one. But with the Ministry of Public Health here in Thailand, a lot of our activities are focused on trying to identify the cases of avian influenza in humans when they occur, and to make sure we're not seeing any signs of human-to-human transmission.

And there have been reports of that, though very limited?
Back in September, we had a cluster that was an index case in a daughter, an 11-year-old girl, who transmitted to her mother and her aunt. The reason that was unique was that the mother didn't live in the same household with the daughter, so we could be quite sure in that situation that the mother and the daughter didn't get it from the same chickens. The mother had no exposure to chickens. The only exposure she had was providing bedside care for her daughter when she was sick. So that was an unusual circumstance that allowed us to be quite confident that it was a person-to-person transmission. But luckily, it didn't continue beyond that, and we got the virus, and it wasn't a mutated form of the virus.

So definitively, you are looking for cases of the virus jumping from human to human? That is when alarm bells are going to ring much more loudly?
Every time there is an individual human case, we are concerned. And there's an investigation. Certainly when there's more than one human case in a cluster, that's of more concern, and there's an intensive investigation like what happened here in September. What would be of most concern is if that goes on for generation after generation of human transmission. That has not happened to date.

And if that were to happen, would that be very difficult to contain?
No one has ever tried to contain an influenza pandemic at its source before. But there are some theoretical reasons now to believe that it might be possible to do that, if we can move quickly enough. And the SARS experience in Asia gave people some encouragement that this kind of potential pandemic can be contained, with good quarantine and public health measures.

So the public health authorities in this part of the world are thinking in a different way than people have in the past about pandemic influenza, and beginning to think realistically about the possibility of trying to contain a pandemic before it spreads. Countries in this area as well as the U.S., have just begun to grapple with the logistics of trying to contain a pandemic at its source.

It sounds like this will take a lot of work, and a lot of money.
It's not beyond the realm of possibility. The last calculations we went through are that you would need somewhere between a hundred thousand and a million courses of Oseltamivir (an antiviral medication) on standby, ready to go. That's a huge number of courses of this antiviral drug, but it's not beyond the reach of some countries.

But while that antiviral might have an impact on avian flu, we don't know that that would be the end of it. Right?
Well the idea is that if we were to detect the first human-to-human spread of this virus, that what you would want to do is have a prepositioned stock of , with a lot of people trained in how to get it out there and administered. And you would go to that area, and you would administer  to all of the cases and all of the contacts of those cases, and what we now know from some of our modeling exercises is that that has the ability to damp down that epidemic and to potentially at least, prevent it from spreading to the rest of the world.