Sequence analysis of related low-pathogenic and highly pathogenic H5N2 avian influenza isolates from United States live bird markets and poultry farms from 1983 to 1989

The last highly pathogenic outbreak of avian influenza in the United Stares was caused by an H5N2 influenza virus in Pennsylvania and New Jersey in 19 83-84. Through a combined federal and state eradication effort, the outbrea k was controlled. However, in 1986-89, multiple H5N2 viruses were isolated from poultry farms and the live bird markets (LBMs) in the United States. T o determine the epidemiologic relationships of these viruses, the complete coding sequence of the nonstructural gene and the hemagglutinin protein sub unit 1 of the hemagglutinin gene was determined for 11 H5N2 viruses and com pared with previously available influenza sequences. The H5N2 isolates from 1986-89 were all closely related to the isolates from the 1983-84 Pennsylv ania outbreak by nucleotide and amino acid sequence analysis for both genes , providing additional evidence that the Pennsylvania/83 (PA/83) virus line age was not completely eradicated. The PA/83 lineage also had a large numbe r of unique amino acid changes not found in other avian influenza viruses, which was suggestive that this lineage of virus had been circulating in pou ltry for an extended period of rime before the first isolation of virus in 1983. High substitution and evolutionary rates were measured by examining t he number of nucleotide or amino acid substitutions over time as compared w ith the index case, CK/PA/21525/83. These rates, however, were similar to o ther outbreaks of avian influenza in poultry This study provides another ex ample of the long-term maintenance and evolution of influenza viruses in th e U.S. LBMs and provides further evidence of the connection of the LBMs and the Pennsylvania 1983 H5N2 outbreak.