Credit HAIRS Report
#17,481
Unlike South America - which has reported thousands of marine mammals killed by avian flu over the past 6 months - the UK has only reported a couple of dozen confirmed non-avian wildlife infections.
Their numbers, like those reported in the United States and elsewhere, are thought to represent only a fraction of the true number of infections in the wild. Most dead terrestrial animals are never recovered (or tested), and marine mammal losses are even harder to assess.
Despite these limitations - and the reluctance of many countries around the world to report on avian flu (and other emerging threats) at all - it is pretty safe to assume that the H5N1 virus hasn't yet acquired the ability to spread efficiently in humans or other mammalian species.
And as we've discussed often, there may be some as-yet undefined species barrier that protects us. Or, the virus may simply not have stumbled upon the right combination of genetic changes that would allow it to spread as a pandemic virus.
Time, as they say, will tell.
Due to it length, I've only posted some excerpts from the HAIRS report. Follow the link to read it in its entirety. I'll have a bit more after the break.
Research and analysis
HAIRS risk assessment: avian influenza A(H5N1) in non-avian UK wildlife
Published 2 June 2023Summary
Avian influenza (AI) is an infectious disease of birds caused by the influenza A virus. Birds are the hosts for most AI viruses (AIV), and a variety of influenza subtypes, including AI A(H5N1), can be found in birds, particularly in waterfowl and shore birds. Domestic poultry are especially vulnerable, and the (Continue . . . )virus can rapidly cause epidemics in flocks. In October 2020, highly pathogenic AI A(H5N1) clade 2.3.4.4b was detected in Europe, after re-assortment of AI A(H5N8) with wild bird lineage N1 viruses. Since October 2021, AI A(H5N1) clade 2.3.4.4b has become the dominant AI subtype detected in wild and captive birds across Europe and the UK, with a relatively stable genotype.
The virus has now been reported from wild birds and poultry across Africa, Asia, North and South America, Europe and the Middle East. Globally, there has been an increased spillover to non-avian species including wild terrestrial and marine mammals, likely as a result of the increased environmental pressure from the thousands of wild birds infected, rather than as a result of increased viral affinity for mammalian cells.
Positive detections of AI A(H5N1) have been identified in a range of animals, mostly from the Carnivora family. In the UK, and as of March 2023, retrospective testing of samples collected since 2021 revealed positive detections in red foxes, Eurasian otters, common and grey seals, harbour porpoises and common dolphins. These were the first detections of AI A(H5N1) in non-avian UK wildlife. Although these findings appear sporadic and isolated incidents, potential mammal-to-mammal transmission of AI A(H5N1) has recently been described in farmed mink in Spain, with genetic analysis revealing an uncommon mutation (T271A) in the PB2 gene which may enhance influenza A viral activity in mammalian host cells.
Where AI A(H5) subtypes circulate in poultry or wild birds, then sporadic human cases should not be unexpected in people with close contact or high levels of exposure. This is particularly evident for Asian lineage AI A(H5N1), with 868 human cases, including 457 deaths, being reported from 21 countries between January 2003 and January 2023. Where Eurasian lineage AI A(H1N1) clade 2.3.4.4b is concerned, from 2020 to the end of December 2022, 6 human cases were reported, globally. All these cases had exposure to infected poultry. To date, there are no reported transmission events of AI A(H5N1) from non-avian infected wildlife to humans.
This risk assessment will focus predominantly on AI A(H5N1) clade 2.3.4.4b as this is the dominant subtype detected in wild and captive birds across Europe and the UK at the time of writing.
Assessment of the risk of infection in the UKProbability
General UK population: Very Low
The probability of infection would be considered Low for those exposed to infected live or dead non-avian wildlife.Impact
The impact on the general UK population would be considered Very Low, while it would be considered Low for high risk groups (for example individuals with occupational exposure to infected wildlife and/or immunocompromised or paediatric cases).
Level of confidence in assessment of riskSatisfactory.
The majority of mammal cases are of the order Carnivora. While they may not all be recognised as commonly predating live or dead avian species, direct contact with a contaminated environment is also a possible transmission route. Without direct observational studies or environmental sampling in areas in the vicinity of known infection, it cannot be proven that mammal-to-mammal transmission is not occurring.
Given human detections of AI A(H5N1) clade 2.3.4.4b are rare, there is a paucity of evidence on what risk factors may increase disease susceptibility, severity and poorer clinical outcomes in human cases. For those cases reported, clinical disease has ranged from mild to severe. There is possible under-ascertainment of cases, particularly in instances where mild disease manifests.
Admittedly, the UK ranks pretty far down the list of countries where we would expect pandemic H5N1 to take off, but it has the virtue of better surveillance and more open reporting than many places around the world.
Even so, they cite a number of instances in today's report where there is a `paucity' of evidence or data available. Risk assessments on emerging threats are always hindered by incomplete or inconsistent information.
Complicating matters, as the H5 virus spreads geographically it continues to diversify into new genotypes (see Novel Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus in Wild Birds, South Korea) and new subtypes (see CIDRAP Canada reports first H5N5 avian flu in a mammal; US reports more H5N1 in animals).
Most of this evolution goes on out of our sight. Just as what is happening in the high latitude summer roosting areas right now won't be apparent until migratory birds make their return in the fall.
Which was followed a week later by a report (see Study: Seroconversion of a Swine Herd in a Free-Range Rural Multi-Species Farm against HPAI H5N1 2.3.4.4b Clade Virus) at a `mixed species' farm (poultry & swine) in Italy.
But the testing of swine herds is only rarely done, and some countries are not inclined to share results for political, economic, or societal reasons. It is just one of many blind spots we have.
Despite all of these concerns, there are no guarantees that H5N1 will spark the next pandemic. It is just one of many plausible contenders, but it appears to have the most momentum now, which is why we focus on it so much.
Six months from now, we could easily be looking at a completely different threat. The only thing guaranteed is that - ready or not - there will be another pandemic in our future.
