Highly pathogenic avian influenza viruses with low virulence for chickens in in vivo tests.

ABSTRACT

Four avian influenza viruses have been recognized that have genetic coding for highly pathogenic avian influenza viruses, but do not show virulence for chickens. The two different mechanisms that prevent this potential being expressed have been determined for A/chicken/Pennsylvania/1/83 (H5N2) and A/goose/Guandong/2/96 (H5N1), but neither of these applies to A/turkey/England/87-92BFC/91 (H5N1) or A/chicken/Texas/298313/04 (H5N2).