Yesterday (July 5th) DEFRA released an updated outbreak assessment (#28) on the ongoing avian epizootic in the UK and Europe, which highlights the unprecedented shift in H5N1 infection from mostly Anseriformes (waterfowl, such as ducks, geese, and swans) last November to Suliformes and Charadriiformes (shore birds) today.
You can see this remarkable progression in the chart at the top of this blog. Admittedly, much of this shift can be attributed to the departure of migratory waterfowl for their summer high-latitude roosting areas.
But normally - when migratory birds leave for the summer - the HPAI virus falls to very low levels in the local bird population, only to reappear when (or if) infected migratory birds return (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).
This year, and for the first time, we are seeing HPAI H5 being strongly maintained in local (non-migratory) birds, and that means the threat to poultry interests may not wane as much as originally expected over the summer.
Below you'll find a link, and some excerpts, from DEFRA's latest update but you'll want to download the 24-page PDF to read it in its entirety. I'll have a postscript after the break.
Updated Outbreak Assessment #28
Highly pathogenic avian influenza (HPAI) in the UKand Europe
20 June 2022 Ref: VITT/1200 HPAI in the UK and Europe
The species of wild birds affected by HPAI in mainland Great Britain have varied throughout the current 2021 to 2022 season, including a greater variety of wild bird species overall compared to previous seasons. An increasing proportion of birds of prey/raptor (Accipitriformes) and other resident species (Passeriformes, Columbiformes) have become infected as the outbreak has progressed and more recently, many seabirds including gannets, gulls, guillemots and great skua have become infected throughout June 2022 (Figure 2).
Thus gannets (Suliforms) now account for over half the cases. This increased number of cases in sea birds may be in part due to breeding patterns, with auk species such as guillemot now at coastal breeding sites rather than out to sea. Gannets and auks nest in closely packed colonies on cliffs and would be exposed to faeces from other birds in the colony.
For further details, please see the report (updated weekly) on findings of HPAI in wild birds in Great Britain and Northern Ireland. As of 20 June 2022, there has been a total of 43 wild bird HPAI findings from across the Scottish islands of Shetland (29), Orkney (10) and the Western Isles (4). These findings comprise of four Arctic terns, eight common eider ducks, 11 gannets, two great blackbacked gulls, 16 great skua, one unidentified gull and one unspecified goose and were collected between 18 March and 06 June 2022. We are continuing to monitor the situation regarding HPAI in the Scottish islands.
Cases of HPAI H5 in wild birds and confirmations in poultry premises have continued to be reported across Europe and in Great Britain since our last assessment. There have been 1,253 confirmed cases of HPAI H5 in wild birds in Great Britain to 20 June 2022 across a range of species, with multiple detections in wild birds each week (Figure 1).
The wild bird species ‘order shift’ observed between November 2021 and June 2022 (Figure 2) reflects the spread of HPAIV infection from migratory water birds to native, sedentary wild bird species, including now seabird populations, which is unprecedented.
The overall number of detections in wild birds, and wild bird infection pressure, is not decreasing as was perhaps anticipated from previous epizootics (Figure 1).
Even though the migratory waterbirds have now departed the UK some months ago, there are still immunologically naïve, susceptible, resident bird species in the UK which could become infected from residual environmental contamination. The number of susceptible birds will increase as the juvenile birds from this season disperse.
Higher environmental temperatures, together with increasing sunlight intensities will greatly reduce environmental levels of HPAI H5N1 and the associated risks in the summer months. However, it remains to be seen to what level the wild bird risk will fall over the summer. The risk of HPAI H5 infection in wild birds in GB remains at MEDIUM.
The risk of exposure of poultry across the whole of Great Britain is maintained at low (with low uncertainty) where good biosecurity is applied, and at medium (with low uncertainty) where biosecurity is suboptimal. This assessment takes into consideration the Avian Influenza Protection Zone (AIPZ) and assumes that bird keepers are taking the additional biosecurity measures required.
All of this is obviously bad news for local bird populations - and poultry interests may not get a reprieve from the avian influenza threat this summer - but it also illustrates how avian influenza continues to evolve and adapt, and how things we may have rightfully assumed a year ago about H5N1 may not hold true today.
Although it remains primarily a threat to avian species, over the past two years we've seen HPAI H5Nx (clade 18.104.22.168b) gain zoonotic status following a small number of human infections, increasingly spillover into non-avian species, and greatly expand its host range among birds.
Where HPAI H5Nx goes from here is unknowable, but when a virus continually defies expectations, it is well worth our close attention.