Major Global Migratory Flyways – Credit FAO
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Just over 13 months ago, the HPAI H5N8 virus appeared at poultry farms – and in wild and migratory birds – in South Korea, and over the next couple of months managed to spread to more than 3 dozen farms. More than a year later, Korean poultry producers are still fighting skirmishes with this emerging virus.
50 day Spread of H5N8 - Map Credit Japan’s MAFF
Until November of last year, H5N8 stayed pretty much an `Asian’ problem. It turned up briefly in Japan, carried by migratory birds last spring (and again in the fall), was reported in North Eastern China - and has more recently produced a massive outbreak in Taiwan - but had not strayed outside of the far northern half of the East Asian Flyway.
At least, not until early November when it surprised everyone by showing up at a German poultry farm (see Germany Reports H5N8 Outbreak in Turkeys), which was quickly followed by reports in the Netherlands, the UK, and eventually even Italy.
Remarkably, H5N8 had travelled farther in a matter of a few months than the H5N1 virus had managed to do over several years. A history we looked at three months ago in H5N8: A Case Of Deja Flu?
It was only few weeks later that British Columbia reported an outbreak of HPAI H5N2 (see Fraser Valley B.C. Culling Poultry After Detecting H5 Avian Flu), followed two weeks later by the announcement from OIE/APHIS: HPAI H5N8 & H5N2 Detected In Washington State Wild Birds.
This upstart H5N8 virus had done in ten months what its predecessor – HPAI H5N1 – had not been able to do in over ten years; it had crossed oceans and made it to the Americas.
And once here, it had managed to successfully reassort with North American (NA) avian influenza viruses, producing new, highly pathogenic subtypes. In short order wild and migratory birds in six western states (Washington, California, Oregon, Idaho, Utah & Nevada) were discovered to be carrying these viruses (see Oregon Quarantines Another Backyard Flock Over HPAI).
Although only two commercial poultry producers (in California) have been hit with this virus, several smaller backyard flocks have been affected, and the virus constitutes a new, and potentially serious threat to our domestic poultry producers.
The good news is, thus far, we’ve seen no evidence of a serious threat to human health from these viruses, but the CDC remains cautious (see CDC Interim Guidance For Testing For Novel Flu).
All of which serves as prelude to a dispatch in the CDC’s EID Journal, that looks at the arrival, reassortment, and potential impact of these HPAI H5 viruses in the Pacific Northwest.
Volume 21, Number 5—May 2015
Dispatch
Novel Eurasian Highly Pathogenic Influenza A H5 Viruses in Wild Birds, Washington, USA, 2014
Hon S. Ip1, Mia Kim Torchetti1
, Rocio Crespo, Paul Kohrs, Paul DeBruyn, Kristin G. Mansfield, Timothy Baszler, Lyndon Badcoe, Barbara Bodenstein, Valerie Shearn-Bochsler, Mary Lea Killian, Janice C. Pedersen, Nichole Hines, Thomas Gidlewski, Thomas DeLiberto, and Jonathan M. Sleeman
Abstract
Novel Eurasian lineage avian influenza A(H5N8) virus has spread rapidly and globally since January 2014. In December 2014, H5N8 and reassortant H5N2 viruses were detected in wild birds in Washington, USA, and subsequently in backyard birds. When they infect commercial poultry, these highly pathogenic viruses pose substantial trade issues.
The novel Eurasian lineage clade 2.3.4.4 highly pathogenic avian influenza (HPAI) A(H5N8) virus (http://www.who.int/influenza/gisrs_laboratory/h5_nomenclature_clade2344/en/) spread rapidly and globally during 2014, substantially affecting poultry populations. The first outbreaks were reported during January 2014 in chickens and domestic ducks in South Korea and subsequently in China and Japan (1–4), reaching Germany, the Netherlands, and the United Kingdom by November 2014 and Italy in early December 2014 (5). Also in November 2014, a novel HPAI H5N2 virus was reported in outbreaks on chicken and turkey farms in Fraser Valley, British Columbia, Canada (5). This H5N2 influenza virus is a reassortant that contains the Eurasian clade 2.3.4.4 H5 plus 4 other Eurasian genes (polymerase acidic protein subunit, matrix protein, polymerase basic protein subunit [PB] 2, nonstructural protein) and 3 North American wild bird lineage genes (neuraminidase [NA], nucleoprotein, PB1) (5). Taiwan has recently reported novel reassortants of the H5 clade 2.3.4.4 with other Eurasian viruses (H5N2, H5N3).
The appearance of highly similar Eurasian H5N8 viruses in Asia, Europe, and now the United States suggests that this novel reassortant may be well adapted to certain waterfowl species, enabling it to survive long migrations (6). These appearances also represent a major change in Eurasian H5 virus circulation. After the reported spread of HPAI H5N1 virus in Asia, a large, interagency avian influenza virus (AIV) surveillance effort was implemented throughout the United States during April 2006–March 2011 (7). Of nearly 500,000 wild bird samples tested, none harbored Eurasian subtype H5 AIV. The overall prevalence of AIV was ≈11%, and most viruses (86%) were detected in dabbling ducks (family Anatidae) (8). Although H5N8 subtype viruses have been detected previously in the United States, all have been low pathogenicity AIV of North American wild bird lineage.
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Phylogenetic analysis of the H5 clade 2.3.4.4 viruses detected in the United States resulted in 3 major findings (Figures 1, 2; Technical Appendix[PDF - 1.71 MB - 7 pages]). First, the Eurasian lineage avian H5N8 clade 2.3.4.4 virus survived introduction into North America in its entirety. Second, introduction of Eurasian H5N8 virus into North America appears to be independent from introductions of the virus into Europe. Third, the duration of circulation of H5N8 virus in the Pacific flyway (California, Idaho, Nevada, Oregon, Utah, and Washington, USA) is unknown, but it was sufficient for reassortment with low pathogenicity North American lineage wild bird AIV (Figure 1).
Conclusions
The ongoing circulation of these Eurasian HPAI H5 viruses in wild birds considerably alters the potential risks and subsequent consequences for US poultry and wildlife rehabilitation centers. Detection of HPAI H5N8 virus in apparently healthy common teal (A. crecca), Eurasian wigeon (A. penelope), mallard, spot-billed duck (A. poecilorhyncha), and tundra swans (C. columbianus) (3,5) suggests that wild birds may contribute to further spread of this HPAI H5 lineage in North America. However, culling and otherwise disturbing wild birds or their habitats has not been shown to be beneficial in the control of avian influenza (10). The scientifically supported management action (10) is to enhance biosecurity to minimize contacts between poultry, wild birds, and their fomites (10). In addition, hunters should be cognizant of risks from handling potentially infected carcasses (http://www.aphis.usda.gov/animal_health/birdbiosecurity/downloads/USDA_HntrCd_Hi.pdf).
Examination of wild bird surveillance samples collected before December 2014 may provide further insight into the timing and route of introduction of the Eurasian clade 2.3.4.4 H5N8 virus into North America. In addition, enhanced and ongoing influenza surveillance in wild birds and poultry will contribute to a better understanding of the geographic distribution and species involved in the spread of these HPAI H5 viruses. Together, these data may enable waterfowl managers and poultry producers to better assess and manage disease risks. Human infections have not been associated with either virus; however, H5 clade 2.3.4 H5N1 virus has caused human death, so caution is warranted. During preparation of this article, H5N8 was reported in wild birds and poultry along the Pacific flyway; novel H5N2 virus was detected in Idaho, Oregon, and Washington; and another novel reassortant H5N1 was detected in Washington and British Columbia (5). These detections have had major effects on US poultry trade (11).
