in 1997. Since 2004 it has ripped through poultry and wild bird populations across Eurasia, and had a 53% mortality rate in the first 147 people it is known to have infected. Health authorities fear this strain, or its descendent, could cause a lethal new flu pandemic in people with the potential to kill billions.
Flu has been a regular scourge of humanity for thousands of years. Flu viruses each possess a mere 10 genes encoded in RNA. All of the 16 known genetic subgroups originate in water birds, and especially in ducks. The virus is well adapted to their immune systems, and does not usually make them sick. This leaves the animals free to move around and spread the virus - just what it needs to persist.
But sometimes a bird flu virus jumps to an animal whose immune system it is not adapted to. In chickens - originally a forest bird and not a natural host - it causes a moderate disease but can readily mutate to a more severe, highly pathogenic strain. Just such a strain of H5N1 flu, named after its surface proteins, began rampaging through large chicken farms in east Asia sometime before 2003. more...
