Evolution and geographical spread of the Avian Influenza Virus H5N1 Type Asia and the problem of biosecurity

摘要

Various "highly pathogenic" strains of the avian influenza virus H5N1 type Asia evolved in China since 1996, but only one of them spread west. This strain was isolated first in may 2005 from bar-headed geese breeding at the huge mountain salt-water Lake Qinghai in central China and reached Europe and Africa in early 2006. The previous hypothesis, according to which migratoring birds transported the Qinghai strain over long distances, has suffered severely from at least nine arguments.Now it seems highly probable that the Qinghai strain was spread west and thence from one country to the next by human activities.Smaller flocks of free-ranging poultry and aggregations of wild birds must be taken to be more biosecure than large-scale poultry operations. This widely accepted view is not adequately reflected by the German avian flu order from Octobel-18(th) 2007.