If many wild birds harbour avian influenza, why aren large numbers of waterfowl dying?
The strains of avian influenza found in wild birds do not usually make wild birds or domestic poultry sick. The strains that can make domesticated birds very sick and kill them are usually the result of a recombination of strains (a mixing of genes from two or more strains) from wild birds and domestic birds. Asian strain H5N1 likely evolved in domestic birds and crossed back into wild birds, where it is atypically causing disease in wild birds.
