Abstract
A novel highly pathogenic avian influenza virus belonging to the H5 clade 2.3.4.4 variant viruses was detected in North America in late 2014. Motivated by the identification of these viruses in domestic poultry in Canada, an intensive study was initiated to conduct highly pathogenic avian influenza surveillance in wild birds in the Pacific Flyway of the United States. A total of 4,729 hunter-harvested wild birds were sampled and highly pathogenic avian influenza virus was detected in 1.3% (n = 63). Three H5 clade 2.3.4.4 subtypes were isolated from wild birds, H5N2, H5N8, and H5N1, representing the wholly Eurasian lineage H5N8 and two novel reassortant viruses. Testing of 150 additional wild birds during avian morbidity and mortality investigations in Washington yielded 10 (6.7%) additional highly pathogenic avian influenza isolates (H5N8 = 3 and H5N2 = 7). The geographically widespread detection of these viruses in apparently healthy wild waterfowl suggest that the H5 clade 2.3.4.4 variant viruses may behave similarly in this taxonomic group whereby many waterfowl species are susceptible to infection but do not demonstrate obvious clinical disease. Despite these findings in wild waterfowl, mortality has been documented for some wild bird species and losses in US domestic poultry during the first half of 2015 were unprecedented.
Highlights
Between January and July of 2014 the H5N8 Highly pathogenic avian influenza viruses (HPAIV) infected domestic poultry at 212 farms in the Republic of Korea[4,8,9] and was detected in numerous local wild birds[10]
In close proximity to the positive pintail, a H5N8 that was >99% similar to the H5N8 HPAIVs detected in Asia and Europe was found in a captive gyrfalcon (Falco rusticolos) that had fed on wild duck meat[17]
Following the detection of HPAIV in Canada and Washington, a multi-agency study was initiated to examine wild birds throughout the Pacific Flyway. This monitoring effort focused on sample collection from hunter-harvested wild birds in the Pacific Flyway of the United States combined with enhanced wild bird morbidity and mortality surveillance
Summary
Between January and July of 2014 the H5N8 HPAIV infected domestic poultry at 212 farms in the Republic of Korea[4,8,9] and was detected in numerous local wild birds (including both live and dead waterfowl)[10]. In close proximity to the positive pintail, a H5N8 that was >99% similar to the H5N8 HPAIVs detected in Asia and Europe was found in a captive gyrfalcon (Falco rusticolos) that had fed on wild duck meat[17] This group of H5 clade 2.3.4.4 viruses—including European, Russian, Korean, Japanese, Chinese, and North American viruses—has been characterized as intercontinental group A (icA)[9]. Following the detection of HPAIV in Canada and Washington, a multi-agency study was initiated to examine wild birds throughout the Pacific Flyway This monitoring effort focused on sample collection from hunter-harvested wild birds in the Pacific Flyway of the United States combined with enhanced wild bird morbidity and mortality surveillance. The goals of this effort were (1) to identify the distribution of the Eurasian H5 clade 2.3.4.4 viruses in wild birds throughout the Pacific Flyway of the United States, which could aid in determining the risk these viruses posed to US poultry producers and wild bird populations, and (2) to better understand what subtypes and what reassortant viruses were present in the US
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