In this study, carried out in Canada , 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 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 % (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.

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.

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, it 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.

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