Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2003
Publication Date: 12/1/2003
Citation: SPACKMAN, E., SENNE, D.A., DAVISON, S., SUAREZ, D.L. Sequence Analysis Of Recent H7 Avian Influenza Viruses Associated With Three Different Outbreaks In Commerical Poultry In The U.S. 2003. JOURNAL OF VIROLOGY. Interpretive Summary: Avian influenza or bird flu is a highly contagious disease in chickens and turkeys. Bird flu has major economic importance both because the disease can case severe health problems or death in infected chickens and turkeys and through trade restrictions and embargoes on areas where bird flu is found. In general the United States is considered to be free of the most deadly form of the disease; highly pathogenic avian influenza. However a form of the disease which causes only minor health problems, but which still has trade implications, has been routinely found in live-bird markets in New York and New Jersey since 1994. Since 1994 the disease has spread to commercial poultry operations in Pennsylvania on two separate occasions and to Virginia, West Virginia and North Carolina in early 2002. Eradication of the virus from commercial poultry has been very costly. Since the most severe form of bird flu can mutate from the less pathogenic form it is very important to monitor the genetics of the bird flu. In this study four of the eight gene segments of bird flu isolated between 1994 and 2002 from both the live bird markets in New York and New Jersey and from commercial poultry operations in Pennsylvania, Virginia, West Virginia and North Carolina were analyzed. Evaluation of the genetics of bird flu from this region (the Northeast US) demonstrated that the isolates in commercial poultry were highly related to the bird flu in the live bird markets, thus the disease spread from the live bird markets. Additionally, genes which are know to affect disease severity were assessed and it was shown that the genes in the current mild disease form are slowly mutating toward becoming the severe disease form of bird flu.
Technical Abstract: Avian influenza viruses of the H7 subtype have been routinely isolated from the live-bird markets (LBMs) in the Northeast United States since 1994 and have spread to the commercial poultry industry on at least three occasions. In this study we performed genetic analysis of the hemagglutinin (HA), neuraminidase (NA), matrix (MA) and non-structural (NS) genes of H7 AIV isolated between 1994 and 2002 in the LBMs and from the outbreaks in commercial poultry. Phylogenetic analysis of all four genes demonstrates that the AIV isolates from the outbreaks in commercial poultry were closely related to the viruses circulating in the LBMs. Phylogenetic analysis also reveals a chronological assortment and close relationship of the HA gene from all of the H7N2 viruses. Conversely, the NA, MA, and NS genes show evidence of extensive reassortment during the first several years, but after 1996, a single gene lineage for each became established despite continuous introductions of other virus subtypes in the LBMs. Also, since 1994 two distinguishing genetic features developed in this AIV lineage; a 17 amino acid deletion in the NA protein stalk region and an eight amino acid deletion in the HA1 protein. Furthermore, analysis of the HA cleavage site amino acid sequence, a marker for pathogenicity in chickens and turkeys, shows a progression toward a cleavage site sequence that is closer to fulfilling the molecular criteria for a highly pathogenic AIV. This study provides an example of AIV evolution over an eight year period in non-natural avian host.