Sometimes good timing is everything.
Published just two days before HPAI H5 was confirmed for the first time in North America’s Mississippi Flyway (see HPAI H5N2 In A Minnesota Turkey Farm followed 4 days later by Missouri Dept. Ag. Statement On Avian Flu At Missouri Turkey Farm), we have a study that looks at the spread, reassortment, and persistence of (low path) avian flu viruses over three seasons in the Mississippi Migratory Flyway (MMF).
The MMF runs from Northern Canada south to the southern tip of Argentina, and encompasses 2/3rds of the continental United States. It is bordered (and overlapped) on the west by the Pacific Flyway, and on the east by the Atlantic American Flyway.
While these flyways are predominately north-south corridors, their overlapping allows for a lateral (east-west) movement of avian viruses as well – often via shared nesting areas and ponds. We’ve recently seen the abrupt move east of HPAI H5 from the Pacific Flyway into the Mississippi Flyway.
First the abstract from the study (which, alas, is behind a pay wall) after which I’ll be back with a bit more.
J Virol. 2015 Mar 4. pii: JVI.03249-14. [Epub ahead of print]
Fries AC1, Nolting JM2, Bowman AS2, Lin X3, Halpin RA3, Wester E3, Fedorova N3, Stockwell TB3, Das S3, Dugan VG3, Wentworth DE3, Gibbs HL4, Slemons RD2.
While geographic distance often restricts the spread of pathogens via hosts, this barrier may be compromised when host species are mobile. Migratory waterfowl in the Order Anseriformes are important reservoir hosts for diverse populations of avian-origin influenza A viruses (AIVs) and are assumed to spread AIVs during their annual continental-scale migrations. However, support for this hypothesis is limited and rarely tested using data from comprehensive surveillance efforts incorporating both the temporal and spatial aspects of host migratory patterns.
Over three autumn migratory seasons we conducted intensive AIV surveillance in waterfowl using the North American Mississippi Migratory Flyway (MMF). Viral isolates (n=297) from multiple host species were sequenced and analyzed for patterns of gene dispersal between northern staging and southern wintering locations. Using a phylogenetic and nucleotide identity framework, we observed a greater amount of gene dispersal within rather than between the other three longitudinally identified North American flyways. Across seasons, we observed patterns of regional persistence of diversity for each genomic segment along with the limited survival of dispersed AIV gene lineages. Reassortment increased with both time and distance resulting in transient AIV constellations.
This study shows that within the MMF, AIV gene flow favors spread along the migratory corridor within a season and that intensive surveillance during bird migration is important to identify virus dispersal on time scales relevant to pandemic responsiveness. In addition, this study indicates that comprehensive monitoring programs to capture AIV diversity are critical to provide insight into AIV evolution and ecology in a major natural reservoir.
- [PubMed - as supplied by publisher]
This study describes the MMF as being an efficient conduit through which avian viruses can intermix, propagate, and spread.
With the recent introduction of HPAI H5 viruses into this avian population – and several new reassortant viruses already detected (H5N8, H5N2, H5N1) – this suggests the potential for additional HPAI subtypes to emerge cannot be ignored.
How viruses shuffle their genes (reassort)
While human infection with these recently emerged H5 viruses have not been reported, they are related to H5 subtypes that have caused severe (even fatal) infections before. Therefore, the CDC is taking a cautious approach, and a couple of weeks ago released CDC Interim Guidance On Antiviral Chemoprophylaxis For Persons With Exposure To Avian Flu and CDC Interim Guidance For Testing For Novel Flu.
Last month, in EID Journal: Novel Eurasian HPAI A H5 Viruses in Wild Birds – Washington, USA, we looked at an early dispatch that warned:
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.
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.
This study also cited three major findings:
First, the Eurasian lineage avian H5N8 clade 18.104.22.168 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).
Although the ultimate fate of HPAI H5 in North America’s wild and migratory birds is unknown, thus far it appears to be thriving in its new found environment. It has produced several new reassortants, it has infected commercial farms in at least three states, and as yet, shows no signs of dying out.
For now, the USDA advises:
All bird owners, whether commercial producers or backyard enthusiasts, need to continue practicing good biosecurity, preventing contact between their birds and wild birds, and reporting sick birds or unusual bird deaths to State/Federal officials, either through your state veterinarian or through USDA’s toll-free number at 1-866-536-7593.