Abstract

A United States interagency avian influenza surveillance plan was initiated in 2006 for early detection of highly pathogenic avian influenza viruses (HPAIV) in wild birds. The plan included a variety of wild bird sampling strategies including the testing of fecal samples from aquatic areas throughout the United States from April 2006 through December 2007. Although HPAIV was not detected through this surveillance effort we were able to obtain 759 fecal samples that were positive for low pathogenic avian influenza virus (LPAIV). We used 136 DNA sequences obtained from these samples along with samples from a public influenza sequence database for a phylogenetic assessment of hemagglutinin (HA) diversity in the United States. We analyzed sequences from all HA subtypes except H5, H7, H14 and H15 to examine genetic variation, exchange between Eurasia and North America, and geographic distribution of LPAIV in wild birds in the United States. This study confirms intercontinental exchange of some HA subtypes (including a newly documented H9 exchange event), as well as identifies subtypes that do not regularly experience intercontinental gene flow but have been circulating and evolving in North America for at least the past 20 years. These HA subtypes have high levels of genetic diversity with many lineages co-circulating within the wild birds of North America. The surveillance effort that provided these samples demonstrates that such efforts, albeit labor-intensive, provide important information about the ecology of LPAIV circulating in North America.

Highlights

  • Waterfowl and shorebirds are regarded as natural reservoirs for avian influenza A viruses (AIV) [1,2]

  • While clinical signs are generally absent in wild bird hosts infected with AIV, these viruses are of interest to agricultural operations because they can cause disease and loss of production in poultry

  • Two virulence phenotypes have been described for AIV based on their pathogenicity in poultry: low pathogenic avian influenza viruses (LPAIV) and highly pathogenic avian influenza viruses (HPAIV) [6]

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Summary

Introduction

Waterfowl and shorebirds are regarded as natural reservoirs for avian influenza A viruses (AIV) [1,2]. Since 1997 Southeast Asian strains of HPAIV H5N1 have been responsible for high mortality in domestic poultry, as well as causing severe disease in some wild birds and mammals, including humans [9]. While a primary goal of this surveillance effort was early detection of Asian strain HPAIV H5N1 in the U.S, a secondary goal was to characterize LPAIV subtypes circulating in the U.S, assess phylogenetic relationships within each sampled subtype, and investigate potential intercontinental gene transfer [12,17,18,19,20,21,22,23,24,25,26,27,28,29]. North America and 3) to examine geographic distribution of HA subtypes across North America

Materials and Methods
H9 H10 H11 H12 H13 H16
Results and Discussion
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