The last 5 Avian Flu Seasons Compared - Credit ECDC
#16,130
Following Europe's 2016-2017 record setting avian epizootic, avian flu activity in wild birds and poultry declined markedly until the fall of 2020 (see chart above), which saw the beginnings of a resurgence in avian flu both in Europe and in Asia.
Highly Pathogenic Avian Influenza (HPAI) activity has varied greatly over the past couple of decades, with both highs and lows, and a continual shifting of dominant subtypes and clades.
- In the early years of the first decade of the 21st century, H5N1 reigned supreme - at first only in Southeast Asia - and then breaking out into Europe, the Middle East, and Africa between 2005-2007. By 2010, Egypt became the world's hotspot for H5N1, and in 2015 Egypt saw the worst human outbreak on record.
- In 2013, LPAI (and later HPAI) H7N9 emerged in China, sparking 5 consecutive years of serious outbreaks in humans, until a new H5-H7 poultry vaccine was deployed nationwide in 2017 which has - at least temporarily - stopped that virus.
- A year later HPAI H5N8, and HPAI H5N6 both emerged in Asia, with H5N8 spreading the fastest, but was not associated with human infection. H5N6 - which remained in China, Vietnam, and Laos - has caused dozens of serious human infections.
These ongoing evolutionary changes probably explain why Egypt and Indonesia - both previous hotspots for H5N1 human infections - have scarcely reported any cases in years, while last spring Russia reported the first confirmed human infections (n=7) from HPAI H5N8 on record.
The only constant with avian flu is change.
Which means we never know what the next fall migration will bring. Migratory birds, who spend their summers congregating in their high latitude roosting spots, can easily share avian viruses, and then carry them thousands of miles during their annual southbound trek (see Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1).
Last fall, the return of HPAI H5N8 after 3 relatively quiet years was seen as primarily a risk to wild or captive birds, and the poultry industry. This year, with fresh evidence that H5N8 has some zoonotic potential (see CDC Adds Zoonotic Avian A/H5N8 To IRAT List), the stakes are somewhat higher.
There are always concerns that China's H5N6 - which has recently sparked an uptick in human infections - could expand its range beyond southeast Asia, or H7N9 or H5N1 could mount a resurgence, or perhaps a new subtype will emerge.
With the earliest arrival of migratory birds in Northern Europe, and northern Asia, expected in the next few weeks, yesterday the UK's DEFRA published two major reports on avian influenza.
The first is a lengthy (234 page) overview of last year's epizootic in the UK, including details on species jumping by H5N8 to foxes and seals. This is an exhaustive after-action report, of greatest interest to epidemiologists, but I've posted a small excerpt on their analysis of HPAI H5N8 below.
November 2020 to April 2021: High pathogenicity avian influenza H5N8 and H5N1 outbreaks in Great Britain
PDF, 8.66MB, 234 pages
The GB viruses were assessed for zoonotic potential using previously applied genetic analyses and it can be concluded that all the viruses are still essentially avian viruses, with no specific increased affinity for mammalian species including humans.
The unusual detection of H5N8 of avian origin in four seals and a fox that had been brought as casualties from the wild and which were being held in close proximity to infected wild swans, while all were undergoing treatment in a rehabilitation centre, indicated that cross-species transmission can occur should conditions allow.
However, again thorough analysis of genetic data generated from samples taken in the investigation of this isolated event indicated that no significant adaptive genetic changes had occurred and that the risk of human infection from this virus remained low.
Reports of human infection with H5N8 in Russia are documented although again genetic evaluation of material recovered did not indicate strongly adaptive mutations. 8 +
A broader genetic comparison of sequence data from international outbreaks demonstrated high sequence identity with wild bird subtype H5N8 clade 2.3.4.4b sequences from Iraq, the Netherlands, Germany, the Russian Federation and the Republic of Kazakhstan from September-November 2020 with the most likely ancestral virus being from a common ancestral virus to that responsible for spread across Middle East/Central Asia.
Again, this assessment suggests that this virus has been recently introduced into the UK through migratory wild birds entering the UK as part of their winter migration. All sequences identified during this outbreak form a single genetic group within clade 2.3.4.4b and are genetically distinct from H5N8 European wild bird isolates from early 2020 and suggests a separate introduction into Europe. Further, these isolates are distinct from those H5N8 viruses detected in the UK in 2016-2017. Either direct or indirect interaction with wild birds or infectious material excreted from wild birds is considered to be the likely source of infection.
The second report is the latest update on avian influenza activity in the UK and Europe (dated Aug 12th). While avian flu activity has sharply decreased since spring, it has not gone away completely, and the annual fall migration is only a few weeks away.
Updated Outbreak Assessment #25Highly pathogenic avian influenza (HPAI) in the UK,and Europe
12 August 2021
Following the unprecedented epizootic of highly pathogenic avian influenza (HPAI) H5 during autumn/winter 2020/2021, there have now been two reports of HPAI H5 in wild birds in the United Kingdom (UK). Three Great Skua (Stercorarius skua) carcasses found on Fair Isle (Shetland, Scotland) have tested positive for HPAIV H5, with one testing positive for HPAIV H5N1. Another Great Skua carcass was found on the Flannan Isles and also tested positive for HPAI H5N1.
There have been no new cases of HPAI in poultry, or in captive birds, in the UK since March 2021.
In Europe, including France, Poland, Czech Republic and Denmark, cases of HPAI H5N8 have continued to be reported sporadically in poultry. HPAI H5 findings in wild birds in Europe have greatly decreased since the peak in March, although the virus is still present in wild water birds along the Baltic coasts. The Netherlands have reported six cases of H5N8 in young Greater White-Fronted Geese (Anser albifrons), found dead in a wetlands area in the Eemdijk region on 3 August 2021.
Germany has reported a further four cases of HPAIV in wild birds since the end of July, although these have not yet been reported by OIE. All of the German wild bird cases were in the Niedersachsen area in the north-west with three H5N8 and one H5N1. Further north in Europe, H5 HPAIV has been reported in wild birds in Finland and Norway. Finland have reported five wild bird cases this week, two H5N8 from mid-July and three H5N1 including a Herring gull (Larus argentatus) from late July. Also, Norway has reported one H5N8 case in a Northern eider duck (Somateria mollissima) found on 29 July 2021.
Situation Assessment
The epizootic of HPAI H5 in Europe in autumn/winter 2020/2021 was unprecedented both in the number of neuraminidase (N) subtypes and the number of wild birds affected. While many poultry outbreaks and wild bird cases were reported in European countries, the UK reported 24 outbreaks in poultry and captive birds. Of these most were HPAI H5N8 in England, with Scotland, Wales and Northern Ireland reporting two, one and two HPAI H5 outbreaks respectively as described fully in our previous report (Avian influenza (bird flu) in Europe, Russia and in the UK - GOV.UK (www.gov.uk)). In total, 320 HPAI H5 cases have been reported in wild birds in the UK over the autumn/winter/spring 2020/2021 epizootic, with most of those in England, and only a few in Scotland, Wales or Northern Ireland.
There have been no new cases of HPAI H5 in poultry or in captive birds (to 13 August 2021) in Great Britain (GB) since 31 March 2021, and no new cases in poultry in Northern Ireland since 12 January 2021. There have been two new reports of HPAIV H5 cases found in wild birds in the UK in July 2021; the first involving three Great Skua (Stercorarius skua) carcases found on the Fair Isle (Shetland, Scotland) on 20 July 2021 and the other one Great Skua carcass found on the Flannan Isles on 27 July 2021. This is the first time HPAI has been reported in Great Skua in the UK during the current (2020/2021) HPAI H5 epizootic, and these Scottish islands represent new locations of infection.
(SNIP)
Conclusion
The risk of HPAI H5 incursion in wild birds remains at LOW (event is very rare but cannot be excluded). Given all factors with ongoing detections in wild bird populations not only in central Asia and southern Russia, but also nearer to the UK mainland in the remote northern Scottish Isles and the Netherlands, the risk level may well increase through the autumn.
We will continue to closely monitor the situation. The risk of poultry and captive bird exposure to HPAI H5 across the whole GB is still LOW (with MEDIUM uncertainty) where biosecurity is sub-optimal, and LOW (with LOW uncertainty) where stringent biosecurity measures are applied. It is particularly important that stringent adherence to biosecurity measures are maintained as summer progresses into autumn, so as to prevent disease being introduced to poultry and captive birds, through contaminated fomites and environmental exposure.
The truth is, we won't know what this winter will bring - in the UK, or anyplace else in the world - until it happens. Some years we get lucky, and avian influenza is a no show. Other years, it arrives with a vengeance.
While Asia and Europe have the highest frequency of HPAI outbreaks, the United States and Canada are not immune, as was demonstrated over the winter of 2014-2015 (see map below), when H5N8 affected more than 220 farms more than 50 million commercially raised birds were lost or destroyed.
EID Journal: Introduction of Eurasian-Origin Influenza A(H8N4) Virus into North America by Migratory Birds
PLoS One: North Atlantic Flyways Provide Opportunities For Spread Of Avian Influenza Viruses
EID Journal: Reassortment in Wild Birds in Alaska before H5 Clade 2.3.4.4 Outbreaks
