Transmissibility of two avian influenza a viruses (H7 N6) between chickens.

Differences were demonstrated in the transmissibility of two strains of avian influenza virus among chickens. One strain, A/duck/Victoria/76 (H7N6) spread quickly and infected all incontact chickens, whereas A/chicken/Victoria/75 (H7N6) spread slowly and failed to infect all incontact chickens. These strains were isolated in the same locality at about the same time in a region where the viruses, and the disease fowl plague, had not been previously recognised.