Recombination Resulting in Virulence Shift in Avian Influenza Outbreak, Chile

摘要

Influenza A viruses occur worldwide in wild birds andare occasionally associated with outbreaks in commercialchickens and turkeys. However, avian influenza viruseshave not been isolated from wild birds or poultry in SouthAmerica. A recent outbreak in chickens of H7N3 low path-ogenic avian influenza (LPAI) occurred in Chile. One monthlater, after a sudden increase in deaths, H7N3 highly path-ogenic avian influenza (HPAI) virus was isolated.Sequence analysis of all eight genes of the LPAI virus andthe HPAI viruses showed minor differences between theviruses except at the hemagglutinin (HA) cleavage site.The LPAI virus had a cleavage site similar to other lowpathogenic H7 viruses, but the HPAI isolates had a 30-nucleotide insert. The insertion likely occurred by recombi-nation between the HA and nucleoprotein genes of theLPAI virus, resulting in a virulence shift. Sequence compar-ison of all eight gene segments showed the Chilean virus-es were also distinct from all other avian influenza virusesand represent a distinct South American clade