Spanish Flu Gives Clues To Deadliness Of Avian Flu

By infecting monkeys with Spanish flu, an international team of scientists think they may have discovered clues as to why the H5N1 Avian flu virus is so deadly to humans.

The scientists report their findings in the current issue of Nature.

The 1918 flu, or "Spanish flu" as it became known, killed over 50 million people worldwide. This latest discovery could help to understand the early progress of the H5N1 Avian flu virus and to develop treatments for the deadly disease which, according to the World Health Organization, has so far killed 63 per cent (161 out of 267) of the people it has infected.

The latest study is the first to examine the effect of the 1918 flu virus in primates. Previous studies have been performed in mice, where it was shown to be highly infectious and lethal.

In this study, which was carried out in Canada, the scientists infected 7 monkeys (macaques) with a reconstructed version of the 1918 flu virus and observed the progress of the illness. They showed symptoms of infection within 24 hours of exposure.

The illness progressed rapidly and within 8 days of exposure the monkeys had such acute respiratory distress that they had to be euthanized.

The 1918 virus was reconstructed from genes recovered from tissue samples that had been preserved from the 1918 pandemic.

The scientists also noticed that the monkeys' normal antiviral response did not protect against the infection. It appeared that the virus itself had switched off the antiviral part of the monkeys' immune system and this lack of protection contributed to the rapid and deadly progress of the disease.

In effect, the monkeys' altered immune system mounted an attack on the respiratory system, filling the lungs with fluid.

A tentative conclusion of the study is that the higher lethality of the 1918 flu virus could be down to its ability to disable the immune system's antiviral response. This is how one virologist member of the study team, Yoshihiro Kawaoka from the University of Wisconsin-Madison, put it: "Somehow, early in infection, this virus does something to the host that allows it to grow really well. But we don't know what that is."

People infected with H5N1 avian flu virus have shown a similar immune system response and rapid progression of the infection.

It could be that the two strains share an ability to switch off the antiviral part of the immune system. If that is so, then this study has made a significant contribution to understanding the progress of the disease in humans too, and opens the door to developing treatments that can be administered in the early stages of the illness, perhaps to re-enable the weakened parts of the altered immune system.

"Aberrant innate immune response in lethal infection of macaques with the 1918 influenza virus."
Darwyn Kobasa, Steven M. Jones, Kyoko Shinya, John C. Kash, John Copps, Hideki Ebihara, Yasuko Hatta, Jin Hyun Kim, Peter Halfmann, Masato Hatta, Friederike Feldmann, Judie B. Alimonti, Lisa Fernando, Yan Li, Michael G. Katze, Heinz Feldmann and Yoshihiro Kawaoka.
Nature 445, 319-323 (18 January 2007)
doi:10.1038/nature05495

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World Health Organization Avian Influenza web site.

Written by: Catharine Paddock
Writer: Medical News Today