Reassortants with equine 1 (H7N7) influenza virus hemagglutinin in an avian influenza virus genetic background are pathogenic in chickens.

Reassortants possessing the hemagglutinin (HA) gene from A/Equine/London/1416/73 (H7N7) [Eq/Lond] and five or more genes from A/Chicken/Pennsylvania/1370/83 (H5N2) [Ck/Penn] were lethal in chickens. This result demonstrates that horses can maintain influenza viruses whose HAs are capable of promoting virulence. Thus, reassortment of equine and avian influenza virus genes could generate viruses that might be lethal in domestic poultry.