The record setting 2016-17 epizootic of HPAI H5 was not the first incursion of a Guangdong lineage HPAI H5 virus into Europe, but it was the largest, and the most damaging.
And almost from the beginning, it was obvious `something‘ was very different about the 2016 virus (see Nov 14th, 2016’s Europe: Unusual Mortality Among WIld Birds From H5N8).
In early January of 2017 we learned that the H5N8 virus had reassorted – likely over the previous summer somewhere in Russia or Mongolia – producing a new, more virulent virus (see EID Journal: Reassorted HPAI H5N8 Clade 220.127.116.11. – Germany 2016).
About the same time, we were also starting to see spin offs of new HPAI subtypes via reassortment (see HPAI H5N5 Detected In German Poultry Operation).
In addition to being far more virulent in wild and migratory birds, this reassorted virus also displayed the ability to infect a much wider range of birds (see ESA 2017 list of 78 species).
Instead of burning itself out quickly – as we’d seen with previous epizootics in both Europe and North America (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl) – this new H5N8 virus showed remarkable persistence and geographic spread – making it’s way into the Middle East, West and Central Africa that same winter, and even the Southern Hemisphere the following spring.
While we’ve seen a handful of analyses ascribing unusual qualities to this 2016 reassorted HPAI H5 virus, the December edition of the CDC’s EID Journal has the most in depth look to date at how Europe’s 20016/17 epizootic differed from previous incursions of the virus.
It’s a long, very detailed, review that points out the 2016/17 epizootic among poultry was 5 times bigger than the 2005/06 outbreak of HPAI H5N1, and 80 times bigger than the 2014/15 initial arrival of HPAI H5N8.
I’ve only included a few brief snippets from the full review, so follow the link to read it in its entirety.
Volume 24, Number 12—December 2018
Pablo Alarcon1, Adam Brouwer1 , Divya Venkatesh, Daisy Duncan, Chrysostomos I. Dovas, George Georgiades, Isabella Monne, Alice Fusaro, Adam Dan, Krzysztof Śmietanka, Vassilios Ragias, Andrew C. Breed, Taxiarchis Chassalevris, Gabriela Goujgoulova, Charlotte Kristiane Hjulsager, Eoin Ryan, Azucena Sánchez, Eric Niqueux, Niina Tammiranta, Siamak Zohari, David A. Stroud, Vladimir Savić, Nicola S. Lewis, and Ian H. Brown
We analyzed the highly pathogenic avian influenza (HPAI) H5 epizootic of 2016–17 in Europe by epidemiologic and genetic characteristics and compared it with 2 previous epizootics caused by the same H5 Guangdong lineage. The 2016–17 epizootic was the largest in Europe by number of countries and farms affected and greatest diversity of wild birds infected.
We observed significant differences among the 3 epizootics regarding region affected, epidemic curve, seasonality, and outbreak duration, making it difficult to predict future HPAI epizootics. However, we know that in 2005–06 and 2016–17 the initial peak of wild bird detections preceded the peak of poultry outbreaks within Europe.
Phylogenetic analysis of 2016–17 viruses indicates 2 main pathways into Europe. Our findings highlight the need for global surveillance of viral changes to inform disease preparedness, detection, and control.
In 2016–17, a total of 1,108 poultry outbreaks were reported in 21 countries in Europe. Extensive farm-to-farm spread, predominantly in ducks, seemed apparent in France, which had > 400 farms affected, and Hungary, with > 200 farms infected (19). Conversely, in 2005–06, a total of 230 poultry outbreaks occurred in 6 countries, mostly located in Romania (86%) and Hungary (13%). In 2014–15, only 13 poultry outbreaks were reported in 5 countries. The estimated number of poultry culled was 8 times higher in 2016–17 than in 2005–06 (Table 1).
The number of wild bird detections was substantially different between epizootics: 1,559 incidents in 27 countries in 2016–17, 487 in 18 countries in 2005–06, and only 5 in 3 countries in 2014–15. Almost half of the wild bird incidents reported in all 3 epizootics were in Germany.
Wild Birds Species and Mass Mortality Events
A total of 49 different wild bird species were reported infected with HPAI H5 virus of the Guangdong lineage in 2016–17, 28 in 2005–06, and 6 in 2014–15 (Table 2,3). Swans (Cygnus spp.), particularly mute swans (Cygnus olor), were the most frequent species infected in 2005–06 (41% of all wild birds) and 2016–17 (20% of all wild birds).
Ducks were the second most common type of wild birds infected. In 2005–06 and 2016–17, tufted duck (Aythya fuligula) was the most frequent duck species detected positive (5% of all wild birds). In 2005–06, a total of 28 (6%) mass mortality events (> 5 birds dead in 1 location) were reported, whereas 112 (7%) mass mortality events were reported in 2016–17; none were reported in 2014–15 (Technical Appendix Figure 2). The number of wild birds found dead by incident was significantly different between epizootics (p < 0.001 by Mann-Whitney U test).
The 2016–17 epizootic of HPAI H5 clade 18.104.22.168 viruses in Europe has 5 times more outbreaks in poultry than observed in the H5 clade 2.2 epizootic in 2005–06 and 80 times more than in the H5 clade 22.214.171.124 epizootic in 2014–15.
This study highlights the unprecedented magnitude of the 2016–17 HPAI H5 epizootic in Europe, in terms of size (both number of poultry outbreaks and wild bird incidents), geographic spread, speed of incidents/outbreaks, and diversity of wild bird species reported infected. As a result, the economic impact is many times higher for 2016–17, which resulted in an >8-fold increase in poultry that died or were culled.
The extent of the 2016–17 H5 epizootic indicates an urgent need to reappraise the effectiveness of surveillance strategies in both wild and domestic birds and to monitor key populations for emergence of viral variants. The differences we observed in the 3 epizootics illustrate the difficulty of predicting HPAI epizootics. However, the temporal peak of wild bird detections preceding the peak of poultry outbreaks at the EU level highlighted the utility of surveillance in wild birds, as observed in other studies (29).
The spatial corridors of HPAI we identified may provide the basis for an increase in targeted surveillance to improve system sensitivity. Although the H5N8, H5N5, and H5N6 European-reassortant viruses have not been shown to infect humans and remain avian influenza–like strains with no evidence of key mammalian adaptation markers (27), their genetic volatility represents a potential threat that requires continuous monitoring and surveillance of virus incidence and genetics to continue to protect public safety.
Dr. Alarcon is a lecturer in animal health economics at the Royal Veterinary College, London. During this study, he was a veterinary epidemiologist at the Animal and Plant Health Agency, United Kingdom, where his role and research focused on the analysis of avian influenza surveillance data in Europe.
While Europe’s HPAI H5N8 was largely supplanted over the winter of 2017/18 by a less virulent HPAI H5N6, it continues to cause outbreaks – and interact with other avian viruses – in Russia, Bulgaria, the Middle East, and Africa.
Despite Europe’s current lull in activity, HPAI H5’s persistence – and its proclivity for reassorting with other viruses – means we can’t know what the future holds for this lineage, or its descendants.
But if the recent past is any guide, with the rapid emergence and evolution of avian flu viruses over the the past decade, we may not have to wait long to find out.