Youth and the avian flu

February 6, 2007 10:39 AM

Reasonable explanation why most victims of avian (and 1918) flu epidemic were young.

The average age of the 160+ victims of the avian flu is in the early twenties with very very few over 50. I believe the statistics were similar for the flu pandemic in 1918. The avian flu might be explained by exposure but I do not think so. Does any one know of any credible scientific explanations as to why this occurs--genetic, status of immune system, etc.

posted by rmhsinc to health (13 comments total)

I remember hearing that a "healthy" immune system could be a liability in the case of the 1918 flu pandemic, since excessive immune reaction caused healthy young people to literaly drown in excessive lung secretion (sorry, but last term might not be correct).
posted by bluefrog at 10:46 AM on February 6, 2007

We don't know. Maybe a cytokine storm.
posted by Zed_Lopez at 10:49 AM on February 6, 2007

From wikipedia:

Scientists have used tissue samples from frozen victims to reproduce the virus for study.[3] Given the strain's extreme virulence and the possibility of accidental escape (or deliberate release) from quarantine, there has been controversy regarding the wisdom of such research. Among the conclusions of this research is that the virus kills via a cytokine storm, which explains its unusually severe nature and the unusual age profile of its victims. (link)
posted by bluefrog at 10:50 AM on February 6, 2007

Bluefrog is correct -- google "cytokine storm" for one explanation of the host specificity of the 1918 pandemic strain.

The other explanation is that the virus' short term evolutionary history in the WWI trenches meant variants displaying quick passage through young men (ie before they got shot) were selected for. Google "serial passage."

Also, check out the Effect Measure blog on Scienceblogs.com for much more discussion of the 1918 strain.

Sorry to not provide full citations.
posted by docgonzo at 10:51 AM on February 6, 2007

Among the conclusions of this research is that the virus kills via a cytokine storm, which explains its unusually severe nature and the unusual age profile of its victims.

Remember a virus does not kill -- death is a byproduct of its attempts to infect cells, co-opt the molecular machinery to make more copies of the virus, escape the cell and be transmitted to a new, susceptible host. Up- and down-regulation of pathogenicity is a by-product of evolutionary processes.
posted by docgonzo at 10:54 AM on February 6, 2007

RE avian flu: there's a theory that some people are genetically susceptible to H5N1.

"There has not been a single case of infection involving husband and wife," Kida said told Reuters. Kida is with the department of disease control at Hokkaido University in Japan.

Kida explained that people infected with H5N1 have a carbohydrate receptor on cells lining their throats. The receptor -- called alpha 2,3 -- is predominantly found in birds. Avian influenza viruses like to bind to this class of receptors to replicate and cause disease.

Human influenza viruses, however, prefer to bind to another receptor called alpha 2,6, which is dominant in humans.

"I think people who are infected with avian strains are special. They must have alpha 2,3 receptors," Kida said.

Further critical discussion on this page.
posted by junkbox at 10:55 AM on February 6, 2007

I would venture a guess that the reason that a majority of the victims of the flu in 1918 were young was because the majority of people at that time were young, because people didn't live as long. Because they died. They were young when they died. Younger than people generally are now. You can't kill old people if there aren't any old people around you know? Because most of the people died while they were young, and so they never grew up to be old people. You know what I am saying? Not the flu victims. I mean they were young too, we've established that. But other people died before becoming old, of other things, and so they couldn't grow old and then die of the flu. Like Bob was always going to die, but he died at age twelve of, say, measles, and then he would have lived through his younger years until age sixty, and then died of the flu in 1918, but he couldn't because he died at age twelve of the measles, as was a common occurence in that day and age. I assume. I don't know. It is just a theory.

Further extrapolation from this theory just ties it all in if you think about it. Because where have the people who died of the avian flu died at? Countries with a young life expectancy right? Probably right? So, they are now like other people were in 1918. So they don't have as many old people, because people tend to die younger, which means that there aren't as many old people to die of the flu, so young people die instead. I really think that I may be on to something. I think that I am right.
posted by ND¢ at 11:15 AM on February 6, 2007

I've read that many children were orphaned as the result of the 1918 flu pandemic. It doesn't seem to be the case with Avian flu though.

Do children and the elderly not experience cytokine storm?

I've also read that there was a similar strain of the 1918 flu between 1908-1918. Some theorize that children may have developed some immunity. But why not adults? More info here, on page 36. I typed the word "young" in the "search this book" bar.
posted by LoriFLA at 11:23 AM on February 6, 2007

Do children and the elderly not experience cytokine storm? (Well there you go. I should have read further.)

"In addition, the H5N1 strain caused immune cells from adults to produce higher levels of certain cytokines than similar cells from newborn babies did. The authors say that finding may help explain why Hong Kong's human H5N1 outbreak in 1997 killed 5 of 9 infected adults (older than 12) but only 1 of 9 infected children. That sharp difference in adult and child mortality rates has not been seen in the current wave of H5N1 cases dating to late 2003.

Scientists have suggested that the cytokine storm played a role in the high death rate in the 1918 Spanish flu pandemic and is playing a similar role in human cases of H5N1 infection today. Autopsies of H5N1 avian flu victims in Vietnam and elsewhere have revealed lungs choked with debris from excessive inflammation triggered by the virus. Similar severe lung damage was frequently reported in victims of the 1918 pandemic, which disproportionately killed people with the strongest immune systems—young, healthy adults."

More info here.
posted by LoriFLA at 11:33 AM on February 6, 2007

ND¢, with all due respect, doesn't know what he's talking about. There were plenty of old people around in 1918, just as there had been plenty of old people around before 1918, which was who the flu had always killed. If anything, 1918 represented a low-water mark for young people in Europe, so many of them having died in the war. Anyway, viruses don't kill off people based on the fact that there are lots of them to kill off; they're not rational like that. Very young and old people die of viruses because their immune systems are weak. The Spanish flu killed people in their prime, with strong systems, because of special properties of the virus, not because there weren't lots of people with weakened immune systems it could have killed.
posted by Dasein at 12:13 PM on February 6, 2007

You're right and wrong, Dasein. There were plenty of old people around, and even if we accept the flawed premise that there were "less old people around back then," it doesn't explain why influenzas that appeared before 1918 tended to kill old (and very young) people just like we're used to.

However, the "evolutionary" aspect of disease is well documented. Viruses (and other diseases) do kill off people based on the fact that there are lots of them to kill off; viruses are selected just like other organisms by their effectiveness in living and propogating. If virus A can live and propogate (read: kill organisms) on a population that is larger than virus B's population, it virus A will tend to be around longer, become more virulent, and kill more organisms.
posted by cklennon at 4:18 PM on February 6, 2007

So you're saying that I am a totally genius virologist? Awesome!
posted by ND¢ at 5:26 PM on February 6, 2007

I read The Great Influenza, which is an excellent read if you're looking to learn more about the 1918 flu pandemic.

There are a lot of diseases that strike the young disproportionately - bacterial meningitis strikes down more college age students than any other age group. There's something about the immune system at that age as the body fully matures that leaves it more open to certain infections.

Here's a really good resource on cytokine storms.
posted by grapefruitmoon at 8:10 PM on February 6, 2007