EMERGENCE OF A POTENTIALLY PATHOGENIC H5N2 INFLUENZA-VIRUS IN CHICKENS

Highly pathogenic influenza A viruses periodically infect both humans and nonhuman animals, including chickens. To gain insight into the ori gin of influenza outbreaks in poultry, we investigated two H5N2 viruse s, A/chicken/Pennsylvania/13609/93 (Ck/PA/93) and A/chicken/Florida/25 717/93 (Ck/FLA/93), that had been isolated in live-bird markets in Pen nsylvania and Florida during surveillance studies in 1993. Phylogeneti c analysis of the HA genes of these isolates, as well as H5N2 viruses isolated from ruddy turnstone surfbirds in 1991 (A/ruddy turnstone/Del aware/244/91 [RT/DE/91]) and other known H5 strains, indicated that Ck /PA/93 and Ck/FLA/93 share a common ancestor with RT/DE/91 and did not originate from A/chicken/Pennsylvania/1370/83 (Ck/PA/1370/83), which devastated chicken populations in 1983-1984. Both isolates were nonpat hogenic in chickens by experimental infection and their HA protein (HA D) could not be cleaved into HA1 and HA2 without trypsin. The sequence s at the HA cleavage sites of Ck/PA/93 and Ck/FLA/93 (R-K-T-R) appear to be intermediate between those of virulent and avirulent viruses, ra ising the possibility that a single mutation could promote virulence i n chickens. We therefore recommend eradication of such viruses as soon as they appear. (C) 1994 Academic Press, Inc.