Avian Epizootics In Europe Since 2016/17
Prior to the 2016/17 avian H5N8 epizootic, the impact of HPAI H5 in Europe had been relatively small, usually involving anywhere from a handful to a few dozen widely scattered outbreaks in poultry each year.
That pattern changed dramatically in the fall of 2016 when a recently reassorted clade 188.8.131.52b HPAI H5N8 virus emerged from either Russia or China, producing new, far more virulent virus (see EID Journal: Reassorted HPAI H5N8 Clade 184.108.40.206. - Germany 2016).
Although this 2016 epizootic was followed by two very quiet years (see chart above), clade 220.127.116.11b H5 virus was quietly reinventing itself - first reassorting into a relatively weak H5N6 virus - and eventually into a new, more problematic H5N1 virus which emerged in 2020.
This reassorted H5N1 not only spread more efficiently via migratory birds, it was more lethal to some wild avian species, resulting in huge die offs of birds across Europe. Instead of disappearing completely during the summer of 2021, the virus persisted at low levels, only to return with a vengeance last fall.
The virus also managed to spread westward, across the Atlantic to North America where is has sparked another major epizootic, resulting in the loss of tens of millions of domesticated and wild birds.
And both in Europe, and in North America, we continue to see signs that HPAI H5 is accruing mammalian adaptations (see here, here, here, and here) , which may help make it a bigger threat to human health in the future (see CDC HAN Advisory On Human H5 Infection In The United States).
Once again, we are seeing unusual persistence of avian flu (both in Europe and North America) well into summer, and last week we saw the first report of HPAI Detected In The Arctic (Svalbard), both of which may herald another wave returning in the fall.
HPAI H5 is currently mostly a threat to wild birds, and the poultry industry, and its impact on human health has been minimal. That said, last May the CDC Added Zoonotic Avian A/H5N1 Clade 18.104.22.168b To IRAT List of influenza viruses with at least some pandemic potential.
Viral evolution is a double-edged sword, and we've seen several HPAI H5 viruses lose their virulence, and their threat recede, over the past 2 decades. That's why we haven't heard about human H5N1 infections in former hotspots like Cambodia, Indonesia, and Egypt for years.
Unfortunately, there is no guarantee we'll get as lucky with this iteration of HPAI H5.
Because of this growing threat, the ECDC, along with EFSA, produce a quarterly, highly detailed, overview of avian flu both in Europe, and around the world. Their latest edition runs 67-pages, and is chock full of both surveillance data and analysis.
Due to its length, I've only posted the link and the abstract. I'll have a brief postscript after the break.
European Food Safety Authority,
European Centre for Disease Prevention and Control,European Union Reference Laboratory for Avian Influenza,Cornelia Adlhoch, Alice Fusaro, José L Gonzales, Thijs Kuiken, Stefano Marangon, Éric Niqueux, Christoph Staubach, Calogero Terregino, Inma Aznar, Irene Muñoz Guajardo and Francesca Baldinelli
The 2021–2022 highly pathogenic avian influenza (HPAI) epidemic season is the largest epidemic so far observed in Europe, with a total of 2,398 outbreaks in poultry, 46 million birds culled in the affected establishments, 168 detections in captive birds, and 2,733 HPAI events in wild birds in 36 European countries.
Between 16 March and 10 June 2022, 1,182 HPAI virus detections were reported in 28 EU/EEA countries and United Kingdom in poultry (750), and in wild (410) and captive birds (22). During this reporting period, 86% of the poultry outbreaks were secondary due to between-farm spread of HPAI virus. France accounted for 68% of the overall poultry outbreaks, Hungary for 24% and all other affected countries for less than 2% each. Most detections in wild birds were reported by Germany (158), followed by the Netherlands (98) and the United Kingdom (48).
The observed persistence of HPAI (H5) virus in wild birds since the 2020–2021 epidemic wave indicates that it may have become endemic in wild bird populations in Europe, implying that the health risk from HPAI A(H5) for poultry, humans, and wildlife in Europe remains present year-round, with the highest risk in the autumn and winter months.
Response options to this new epidemiological situation include the definition and the rapid implementation of suitable and sustainable HPAI mitigation strategies such as appropriate biosecurity measures and surveillance strategies for early detection measures in the different poultry production systems. Medium to long-term strategies for reducing poultry density in high-risk areas should also be considered.
The results of the genetic analysis indicate that the viruses currently circulating in Europe belong to clade 22.214.171.124b. HPAI A(H5) viruses were also detected in wild mammal species in Canada, USA and Japan, and showed genetic markers of adaptation to replication in mammals.
Since the last report, four A(H5N6), two A(H9N2) and two A(H3N8) human infections were reported in China and one A(H5N1) in USA. The risk of infection is assessed as low for the general population in the EU/EEA, and low to medium for occupationally exposed people.
Just as Europe's HPAI H5 has likely been ferried north to the high latitude roosting spots for migratory birds in Siberia and the arctic, it is a fair assumption that the virus has been carried by North American migratory birds to their summer roosting areas in the 19-million acre Arctic National Wildlife Refuge.
The $64 question is what happens there?