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Although it is still early in the season, this year's annual migration of birds from China and Siberia, into Europe, the Middle East, and Africa, is being carefully watched following last spring's elevation of HPAI H5N8 to a potential zoonotic threat.
Unlike its Asian counterparts, European HPAI H5Nx viruses had never been viewed as posing a serious public health threat.
But over the past 4 years we've see evidence of increasing mortality among poultry and wild birds, and more recently in mammals (see EID Journal: HPAI A(H5N1) Virus in Wild Red Foxes, the Netherlands, 2021). In February of 2020, Russia announced 7 mild/asymptomatic infections among poultry workers.
Over the past few weeks we've followed reports of HPAI beginning to move out of Russia into Europe, including yesterday's Netherlands: HPAI H5 Outbreak In Poultry In Zeewolde - National Indoor Confinement Order For Commercial Poultry).
Overnight the UK's DEFRA published their first assessment of this fall's avian flu activity, which notes changes in the epidemiology this year, and raises the risk of HPAI H5 incursion to Great Britain from LOW to MEDIUM.
I've only posted excerpts from the 6-page PDF below, so follow the link to read it in its entirety. I'll have a brief postscript when you return.
Preliminary Outbreak Assessment #0
Highly pathogenic avian influenza (HPAI) in the UK,and Europe
26 October 2021 Ref: VITT/1200
HPAI in the UK and Europe Disease Report Since our last report on 15 September, there is evidence that there have been significant changes in the epidemiology of highly pathogenic avian influenza (HPAI) H5 in Europe. While there have been no further HPAI H5N8 outbreaks in captive birds in north-east France, Belgium and Luxembourg since our last report, HPAI H5N1 is spreading in wild birds (namely ducks including Eurasian wigeon and mallard) along the wildfowl migration flyway in northern Germany and Denmark. These species will migrate further west into GB, and many have already arrived with high numbers of wigeon still expected across GB, peaking in December.
Furthermore, this H5N1 strain in wild birds requires full characterisation to determine the genetic relationships in comparison to H5N1 viruses detected in spring/summer to establish if they have derived from local recrudescence or relate to new introductions to Europe of a related or identical virus.
Situation Assessment
The epizootic of HPAI H5 infection in Europe over the autumn/winter season of 2020/2021 was unprecedented both in the number of virus genotypes including multiple neuraminidase (N) subtypes and the numbers and species of wild birds affected (IZSVe 2021a). There were numerous positive HPAI H5 incidents reported in domestic poultry and wild birds through spring and summer particularly in the low countries of north-west Europe and the Baltic Sea coast (namely the Netherlands, Finland and Sweden) with the main focus in Northern Europe. These events were most probably linked to extensive infection pressure from the winter period and environmental survival of virus including near to poultry production premises. The UK reported 24 outbreaks in poultry and captive birds during autumn/winter 2020/2021, as described fully in previous reports (Avian influenza (bird flu) in Europe, Russia and in the UK - GOV.UK (www.gov.uk)).
In the autumn period of 2021 the first H5N1 reported cases were in Barnacle geese (Branta leucopsis) in southern Finland in early September, perhaps representing the start of a new wave of HPAI spreading west in migratory waterbirds. Subsequently Germany has reported H5N1 HPAI to OIE in unidentified wild geese species at Pellworm (Schleswig-Holstein) on its north-west coast (Wadden Sea) detected on 14 October 2021. In addition, there are reports of further cases of H5N1 in wild ducks in north-west Germany (Schleswig-Holstein), Denmark and the Netherlands, with a zoo affected in north-east Germany (Mecklenburg-Vorpommen) (FLI 2021).
The duck species infected in Germany include Eurasian wigeon (Mareca penelope) and Mallard (Anas platythynchos) (IZSVe 2021b). Eurasian wigeon overwinter in large numbers across GB, peaking at over 300,000 birds every December, with numbers steadily increasing through October and November.
Whilst some birds have now arrived in GB, the majority will follow in the next few weeks, having flown through areas in northern Europe now reporting H5N1 HPAI including the Wadden Sea bordering north-west Germany and Denmark. Two poultry outbreaks of H5N1 has also been reported in Europe namely an outbreak of H5N1 in turkeys on 18 October 2021 in northern Italy and an outbreak in backyard birds in the Czech Republic at the end of September (PAFF 2021). Finland has also reported four events of H5N1 detected in late September in Ring-necked pheasants (Phasianus colchicus) including three groups of several thousand birds released as game birds earlier this year.
Elsewhere in Europe, H5N1 has been detected in a White-tailed eagle (Haliaeetus albicilla) in Estonia in mid-October. Further east, Russia has reported 18 H5/H5N1 events in captive backyard/village birds and three H5 outbreaks in poultry farms starting late September/early October. Ukraine has reported an H5 outbreak in backyard birds detected in mid-October. HPAI H5N8 has been reported in a flock of Canada geese (Branta canadensis) in Sweden in mid-October and in two wild birds and one backyard poultry premises in Estonia in late September and mid-October. Serbia and Montenegro reported three H5N8 events in Mute swans (Cygnus olor) detected in late September to mid-October. The map below shows the distribution of HPAI H5 events in poultry, captive birds and wild birds in Europe reported in September and October to OIE. Those events reported in October are distinguished with dots and show the recent westward spread into north-west Europe since the H5N8 captive bird outbreaks in north-east France, Luxembourg and Belgium from September (described in our previous report).
Implications for the UK
The HPAI H5N8 outbreaks described in our last report on 15 September 2021 in backyard birds in Luxembourg, Belgium and France were probably due to residual infectivity from the 20/21 season. They appeared epidemiologically distinct from the usually coastal sites bias (associated with migratory bird stop overs) generally associated with the main autumn migration movements into GB; as such they suggest a relatively small risk to GB through the movement of wild water birds.
However, there is now evidence that the risk of incursion of HPAI H5 in wild birds in GB is increasing. In particular, HPAI H5N1 is spreading in wild birds along the northern coast of Germany, southern Denmark (Wadden Sea) and the Netherlands which is on the migration route for migratory water birds flying to GB.
In addition it should be noted that genetic diversity may be expected given the unprecedented diversity detected within virus subtypes during 2020/21. This H5N1 strain in wild birds in the Wadden Sea requires full characterisation to determine the genetic relationships in comparison to H5N1 viruses detected in spring/summer 2021 to establish if they have derived from local recrudescence or relate to new introductions to Europe of a related or identical virus.
Conclusion
There is evidence that there have been significant changes in HPAI H5 epidemiology in Europe to warrant increasing the risk of incursion of HPAI H5 via wild birds in GB from LOW (event is rare but does occur) to MEDIUM (event occurs regularly).
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. We are in a period of rapid seasonal change with respect to these risks and will continue to closely monitor the situation.
This increase in wild bird risk incursion coincides with the proposed decrease in threshold of collecting reported dead wild birds from five to just one from the list of target species, thereby increasing the sensitivity of detection of the wild bird surveillance scheme. Given all the factors, with ongoing detections in wild bird populations not only in central Asia and southern Russia, but also nearer to GB in northern Germany, Denmark and the Netherlands together with the imminent arrival of more migratory waterfowl, the risk level to GB may well increase further through the autumn and into the winter.
Just as in Europe, there is a need to bolster biosecurity here in the United States (see H5Nx: Why North America Must Remain Alert). The USDA has some advice on how to Defend The Flock at the website below.
