Good health may not protect against H5N1

Understandably, many of us believe that one way to fight a potential bird flu infection is to be in great shape.  Numerous health practitioners are exhorting us to do all those healthful things, so we’ll better our chances against a potential bird flu infection, and vendors are promoting supplements that are presumed to enhance immune function. 

If these ideas catch on, they may bring benefits – but not because they protect against H5N1 or other possible pandemic influenza virus sub-types.  Why is that?  Let’s see how the healthiest populations were affected by bird flu viruses then and now.

Who got hit hardest?

How are those age groups with the most competent immune systems faring so far?  Here is a clue[1] from a few weeks ago:

And here is one from 1918[2]:

It looks like the H1N1 influenza of 1918 and the today’s H5N1 bird flu hits those particularly hard, who are in the age range where one would expect the immune system to be most competent.

Why is this?

This week brought additional laboratory evidence that bird flu is very different from the seasonal human influenza.  When bird flu infects human cells it is much more likely than seasonal flu to grossly exaggerate the response of the immune system.  The resulting destructive overreaction has been called a "cytokine storm."[3] 

Cytokines are messenger substances with which cells instruct each other to perform complex functions such as recognizing and destroying infectious agents.[4]  When this network of chemical messages is disrupted, the body will suffer damage.  If the immune response is too sluggish, a tissue or the entire body may be overwhelmed by an infection.  If the immune system is over-stimulated, “friendly fire” may cause so much “collateral damage” that the body can no longer perform vital functions.  Such is often the case in victims of H5N1.  A more competent immune system will have more “fire power” and thus do more damage.

Confirming evidence

The new study[5] confirms earlier work that showed bird flu viruses to cause the release of such a high amount of inflammatory messenger substances by cells which are supposed to defend us against infections, that not only the infected cells were damaged, but also healthy tissue.[6]  In the study, immune cells called macrophages released about 20 times more inflammatory messenger substances when infected by H5N1 than by human influenza virus, but only in the mature, adult version of these cells. Immature macrophages from newborns did not show this response.

Cytokine storms most likely contributed to the high death rate in the 1918 influenza pandemic and certainly in the human cases of H5N1 infection since 1997. Severe lung damage due to inflammation was found in the lungs of influenza victims then and now. The greatest damage appears to be found in young, healthy adults, the very people with the strongest immune systems. 

A conclusion

Being in good shape does not lessen the need to take other precautions.[7]

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[1] An analysis by Influenza Report of demographic data published by WHO.  http://www.influenzareport.com/ir/figures/ad060530.htm

[2] Taubenberger JK, Morens DM.

1918 Influenza: the mother of all pandemics.

Emerg Infect Dis. 2006 Jan;12(1):15-22.

[3] E.g. Yuen KY, Wong SS.

Human infection by avian influenza A H5N1.

Hong Kong Med J. 2005 Jun;11(3):189-99.

[4] Inflammatory cytokines that are exaggerated by H5N1 include:  IL1α , IL1ß , IL6, IFN-γ. At the same time, levels of the anti-inflammatory cytokine IL10 are decreased.

[5] Zhou J, Law HK, Cheung CY, Ng IH, Peiris JS, Lau YL.

Differential expression of chemokines and their receptors in adult and neonatal macrophages infected with human or avian influenza viruses.

J Infect Dis. 2006 Jul 1;194(1):61-70. Epub 2006 May 26.

[6]  Chan MC, Cheung CY, Chui WH, Tsao SW, Nicholls JM, Chan YO, Chan RW, Long HT, Poon LL, Guan Y, Peiris JS.

Proinflammatory cytokine responses induced by influenza A (H5N1) viruses in primary human alveolar and bronchial epithelial cells.

Respir Res. 2005 Nov 11;6:135. 

[7] E.g.: Grattan Woodson’s “Preparing for the Coming Influenza Pandemic”.

Hardcopy: http://www.amazon.com/gp/product/0757304982/qid=1148613835/sr=1-1/ref=sr_1_1/102-2408134-4740938?s=books&v=glance&n=283155 ,

Or on the web: http://www.fluwikie.com/uploads/Consequences/NewGuideOct7b.pdf