Scientists appear to have solved an enduring mystery surrounding the 1918 outbreak of Spanish flu which killed millions worldwide.
Estimates say the epidemic took 50 million lives, more than the First World War. Unlike most bird flu strains, it was lethal amongst young, healthy people.
A Canadian lab reconstucted the Spanish flu virus from human tissues preserved in the Alaskan permafrost and infected macaque monkeys. Their findings were reported on Thursday in the journal Nature, and should give a better view of how the virus killed humans than earlier work with infected mice.
It turns out that the H1N1 Spanish flu virus (the current bird flu threat is from H5N1, the nomenclature derived from the proteins which coat the virus) killed 50 million by over-stimulating their immune system, causing the lungs to inflame and rapidly fill with liquid. Lead author Professor Yoshihiro Kawaoka of the University of Wisconsin said: "Essentially people are drowned by themselves."
So a young, healthy person with a young, healthy immune system would be a ripe victim for the 1918 strain. Associated Press reports co-author Michael Katze, of the University of Wahington, said: "It was the robustness of the immune system that helped victimize them."
The researchers write that symptoms of the disease appeared within 24 hours of the monkeys' exposure to Spanish flu. They became so ill they were were euthanised after only 8 days of a scheduled 21 day trial.
The type of cascading immune response the virus induced is known as a "cytokine storm". Cytokines are the protein messengers released by cells which modulate the immune system. A comparable cytokine storm was implicated in the disastrous drug trial last year which hospitalised six volunteers.
The team's work to rebuild and study Spanish flu will help understanding of how the rapidly-evolving disease becomes more deadly. The current H5N1 strain appears to have similar immune-fiddling powers in birds. ®