#16,562
Although North America had its own close encounter with HPAI H5Nx (H5N1 & H5N8) during the spring of 2015, which resulted in the loss of nearly 50 million birds, since then this avian virus has primarily been a European and Asian problem.
The virus - at least until 2016 - wasn't able to sustain itself long-term in the wild bird population, and tended to die out over the summer.
Over the past 5 years we've seen increasing persistence of the virus in wild and migratory birds, and more frequent, and more frequent epizootics; particularly in Europe. We've also seen signs that this primarily avian virus has picked up some mammalian adaptations (see Netherlands DWHC Reports another Mammal (Polecat) Infected With H5N1.
Last year, after a handful of documented (but very mild) human infections, HPAI EA H5Nx was elevated to having at least some zoonotic potential (see ECDC/EFSA Raise Zoonotic Risk Potential Of Avian H5Nx).
The risk to humans is admittedly low right now, but that could change over time.
And of course, this year, HPAI H5N1 has crossed oceans (see Preprint: Transatlantic Spread of HPAI H5N1 by Wild Birds from Europe to North America in 2021), turning up in Canada and the United States for the first time in nearly 7 years.
Reminding us that vast bodies of water don't always protect us from distant disease threats.
While the number of commercial poultry farms infected with H5N1 in North America remains quite low (n=2), our last H5 avian epizootic extended well into June. Meaning we've months of potential risk ahead.
But the good news, at least in Europe, is that their avian epizootic - which as been raging since early last fall - appears to have peaked in the second week of January (see chart below). While another wave may occur when migratory birds begin to head later this spring, the following graph shows the recent decline.
Although primarily focused on the UK, the following DEFRA update provides details on H5Nx across all of Europe. I'll return with a postscript after the break.
Updated Outbreak Assessment #1307 February 2022 Ref: VITT/1200 HPAI in the UK and Europe Disease ReportSince our last outbreak assessment on 31 January 2022, there continue to be reports of highly pathogenic avian influenza (HPAI) H5 both in Europe and in the United Kingdom (UK). This includes two further confirmed outbreaks of HPAI H5N1 in domestic poultry and captive birds in the UK.There have been a further two confirmed outbreaks in Great Britain (GB) of HPAI H5N1 in domestic poultry and captive birds since our last assessment, both of which have been in England. One outbreak was in a commercial broiler breeder chicken premises in Hampshire, while the other occurred at a conservation park in Norfolk. There have been no further HPAI H5N1 outbreaks confirmed in Northern Ireland since 24 January 2022 (DAERA 2022).Since 31 January 2022, OIE has reported outbreaks of HPAI H5N1 in domestic poultry in Germany, the Netherlands, Poland and Spain, and one further outbreak of HPAI H5 in domestic poultry in Bulgaria.Wild bird HPAI H5 cases continue to be reported in Austria, Belgium, Finland, Germany, Hungary, Romania, Spain and Sweden. The highest number of wild bird cases reported in the last week was for Germany (54), which has dropped from 71 since the previous week
(SNIP)
Since our last outbreak assessment on 31 January, to 07 February 2022, HPAI H5 has been detected in a further 11 wild bird locations in GB, bringing the total to 182 separate wild bird positive locations, involving 33 different bird species in 63 separate counties (Table 2). There have been eight cases for which the H5 genotype has been identified but the N type has not. These cases are currently undergoing further processing to identify the Neuraminidase genotype strain (H5Nx in Map 2).
(SNIP)
ConclusionCases of HPAI H5 in wild birds and outbreaks in poultry continue to be reported across Europe and also in GB since our last assessment.Total numbers of migrating wild water birds (ducks, geese, and some swan species) will now have peaked in GB and the majority of wintering water birds have now arrived. There have been 614 confirmed cases of HPAI H5 in wild birds in GB to 07 February 2022 across a range of species, including a significant number of resident sedentary birds of species such as mute swan, Canada goose and some raptors indicating that they had been exposed to infection in GB itself. Furthermore, potential bridging species such as pigeons, gulls, pheasants and some raptors have tested positive. In continental Europe, corvids and sparrows which could also serve as bridging species continue to be reported as infected.HPAI H5 is continuing to circulate in both susceptible over-wintering migrant water birds and sedentary wild bird species within GB with a greater number of events likely to be observed around water bird wintering sites. The risk level of HPAI H5 in wild birds is therefore maintained at VERY HIGH across GB.The risk of exposure of poultry across the whole of GB is maintained at MEDIUM (with low uncertainty) where good biosecurity is applied, and at HIGH (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.
The $64 question (to which I have no answer), is whether this new and improved HPAI H5 virus will become endemic in North American birds, as it has in Europe and Asia since 2016.
The fact that HPAI H5 did not return to North America in the fall of 2015 - while welcomed news - was unexpected (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).
Since then, HPAI EA H5Nx has reinvented itself through multiple reassortment events, and - at least in Europe and Asia - appears to be better adapted for long-term carriage by migratory birds.
While future reassortment events could `undo' these functional gains, the possibility exists that avian flu epizootics could become more common in North America in the years to come.
Stay tuned.
