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Q&A : Why Bird Flu Kills
posted by admin on 25/08/06
An interview with Professor Art Reingold from Berkeley’s School of Public Health
WHO GETS BIRD FLU, how do they get it, and who survives and who dies? Art Reingold, a professor and head of the Division of Epidemiology at University of California, Berkeley's School of Public Health, has studied the emergence infectious diseases in the developing world. He talks with the Online Journal's Matt Phillips about important patterns in the fatal cases of H5N1 bird flu, how those trends may shift and what clues epidemiologists use to track diseases.
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WSJ.com: Based on what you've seen of H5N1, what are some of the patterns in the way that it spreads?
Dr. Reingold: Well, I think you have to look at two different issues. One is, Who gets bird flu? And the other is, Among the people who get it, why do some die and others not? So I think those are two separate questions.
In terms of who gets bird flu, obviously -- at the moment at least -- that really reflects overwhelmingly, exposure to infected birds. So the age distribution of who gets bird flu is largely a reflection of who's in contact with infected birds and their secretions. And that tends to be younger people.
First of all, most of that exposure is occurring in developing countries -- where the age of the population is generally young. And secondly whether it's in a workplace setting or whether it's a marketplace or in a yard where there are contaminated poultry, many people who are coming in contact with these infected birds, are young.
So this is not like standard influenza where a good deal of the infection and illness and death is in the elderly. I think the pattern of it being overwhelmingly young people who've gotten infected, at least in part reflects, who is most exposed to infected birds.
Now, among people who get infected, what is the fatality for different age groups? And unfortunately there's only been about 150 people who are confirmed, 150 to 200 people over the past seven or eight years, who have been confirmed as having [been killed by] bird flu. So the numbers are not terribly great in terms of looking at the fatalities in one age group versus to another.
Q: Are you talking in a statistical sense, there might not be a large enough sample?
A: Exactly … Certainly, a number of the people who have died have been quite young, children and young adults -- and I don't think we really understand very well the human immune defense response to this virus.
There is some suspicion that similar to what happened … in 1918 with the big pandemic that people always refer back to, it may be the case that younger healthier people mount a more powerful immune response to this virus and produce what scientifically might be called a "cytokine storm" which basically means a very, very powerful immune response, more so than an elderly person might and that a lot of the damage and the risk of death may relate to the immune response to the virus.
I would say that's a theory, it's really not proven. But there's a suspicion that that happened in 1918. Because in 1918 there's no question that the young, healthy people who got influenza had a much great risk of dying than we typically see with influenza … Most of the deaths typically occur in infants and in the elderly, the infirm, the sick elderly.
So with 1918 pandemic and at least with some of the [H5N1] bird flu cases … there certainly have been fatalities among previously healthy young people and I'm just saying I don't think we have a very good understanding yet of the biology of that. And we don't really have large enough numbers to look at it statistically very well.
Q: Are there any interesting trends that you have seen regarding gender breakdowns of acquisition and fatality?
A: The quick answer is no. Again I think in terms of acquisition it largely reflects who is exposed to contaminated birds. So, obviously, in a household setting sometimes that is young girls and women. So we certainly do have cases in girls and women. In other occupational settings -- people who are killing birds … or things like that -- a lot of those jobs are done by men. So you know my guess that who gets it … is largely more of a question of who is exposed to contaminated birds. And I'm not aware of any real differences in fatalities by male-female breakdown.
Q: What are some of the other issues epidemiologists look at when they're trying to figure out how diseases spread. What are epidemiologist looking at for avian flu to try to get a clue?
A: Well I think for avian flu, we know how it's spread. So fundamentally we know that -- at the moment at least -- it's almost entirely due to … exposure to contaminated birds or their droppings. The concern of course is that it might at some point become a virus that can be more readily transmitted directly from one person to another. And that would be the scenario in which we could potentially have a very serious epidemic or pandemic but that really hasn't happened to any great extent yet.
Now how do we study that or how do we ascertain that … Part of it involves looking at cases of H5N1 influenza in people. [We try] to ascertain whether they all have had exposure to sick birds or infected birds or not. And particularly [we're] looking to see whether there's evidence of transmission from a sick person to either other members of the household or family who may have taken care of that person. Or among healthcare workers in a hospital or clinic who may have taken care of that person. So that's basically one form of epidemiologic evidence people would be looking for, for person to person transmission. [They'd] be looking at the people who take care of people with bird flu.
Q: People who take care of them but were maybe not around for the initial exposure?
A: Exactly. So, in the case of hospital personnel … we can typically be relatively confident that they weren't exposed to the same birds. In the case of family members who have taken care of someone who's ill, obviously there are many instances where the same family members also may have been exposed to infected birds. So among family members it can be very difficult to sort that out. Although obviously sometimes you have a situation where the family-members taking care of somebody who's sick come from a different village or come from a different locale and is really unlikely to have had exposure to the same bird population… Each case … has to be looked at individually to try to ascertain that.
Q: Say the virus did mutate to allow it to be easily transferable among people, what would be some of the patterns you might expect to see?
A: If unfortunately we ever were to move to a situation where there was a lot of person-to-person transfer going on, we would expect to see the entire age spectrum of people involved because people in essence are all susceptible to this virus, people don't have antibodies to this virus. So we would expect to see infections and disease across the entire age spectrum.
Q: Any other key markers you'd be looking for?
A: Obviously influenza can spread very quickly. It did in 1918 when there were more primitive ways of people getting around and so I think we would certainly note a very rapid spread … [increases] in numbers of cases, geographic areas that are involved, things like that.
Write to Matt Phillips at email@example.com
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