|Senne,, Dennis - NAT'L VET SERVS, AMES,IA|
Submitted to: American Society for Virology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2001
Publication Date: July 21, 2001
Technical Abstract: A H7N2 avian influenza virus has been enzootic in the live bird markets in the Northeast United States since 1994. The viruses have been and remain low pathogenic in nature, but the virus did spread to large commercial poultry farms in 1997 causing disease and production losses. Sequence analysis of representive isolates shows that most of the isolates have a hemagglutinin gene from the same lineage suggesting that the gene introduced in 1994 has persisted until today. Changes have occurred in the hemagglutinin including two changes at the hemagglutinin cleavage site and an eight amino acid deletion in the HA1 part of the protein. The cleavage site changes include a Thr to Pro change at the -2 position first observed in 1995, and an Asp to Lys change at the -5 position first observed in 1998. The additional basic amino acid near the cleavage is particularly worrisome because of the increased risk of this virus becoming highly pathogenic. The eight amino acid deletion is predicted to be near the receptor binding site based on molecular modeling. All three changes have become the predominant genetic features of currently circulating viruses. Analysis of the nonstructural and matrix genes suggests that reassortment of internal genes is widespread, presumably with other subtypes of influenza that are also in the market. The nucleotide substitution and evolutionary rates are similar to what is observed in mammalian viruses.