#16,916
While HPAI H5N1 clade 2.3.4.4b - the virus causing our record-setting North American and European avian epizootics - is mostly a threat to wild birds and poultry, we continue to see worrisome reports of spillovers into mammals, often with severe neurological manifestations.
Maine: Seal Deaths Linked To Avian H5N1
Quebec: Seal Deaths Linked To Avian H5N1
Two States (Michigan & Minnesota) Report HPAI Infection In Wild Foxes
Ontario: CWHC Reports HPAI H5 Infection With Severe Neurological Signs In Wild Foxes (Vulpes vulpes)
Netherlands DWHC Reports another Mammal (Polecat) Infected With H5N1
Human infections, have thankfully been very few and mild. Nevertheless, just over 11 weeks ago the CDC Added Zoonotic Avian A/H5N1 Clade 2.3.4.4b To IRAT List.
Just over a week ago, in PrePrint: HPAI H5N1 Infections in Wild Red Foxes Show Neurotropism and Adaptive Virus Mutations, we saw evidence from the Netherlands that Europe's avian H5N1 virus was adapting to its new-found mammalian hosts by acquiring the PB2-627K mutation.The concern is that the more often this virus jumps species, the more chances it will have to acquire host adaptations that will make it better able to spread, and cause disease, in mammals (including humans).
PB2-627K can enable the virus to replicate more efficiently at the lower temperatures (33°C) commonly found in the respiratory tract of mammals, rather than the higher temperatures found in avian gastrointestinal tracts.
While we've seen sporadic spillovers of avian influenza into mammals in the past (see here, here, here, and here), these tended to be one-off, or limited events, often caused by feeding zoo animals infected chicken carcasses. These captive animals had little chance to spread the virus beyond their cages.
The infection and deaths of hundreds of seals in Europe, the United States, and Canada suggests ongoing transmission in the wild, and with that comes an increased risk of adaptive mutations.
Today we've a preprint, published on the BioRxiv website, detailing two genetically distinct waves of HPAI H5N1 spreading in wild and migratory birds in New England in 2022, and the recent spillover of the second wave virus into seals in coastal Maine.
Thus preprint is well worth reading in its entirety, but a couple of important points to ponder. First, the detection of 2 genetically distinct waves of HPAI H5N1 this year in New England reminds us that this virus is a continually evolving threat.
This may help explain The Unprecedented `Order Shift' In Wild Bird H5N1 Positives In Europe & The UK, we looked at last month, and its extended geographic range and persistence into the summer months.
The second point is the unpredictability of all of this - now that it is spreading in a mammalian host - as elucidated in the closing paragraph of this preprint:
Unlike in agricultural settings, outbreaks in wild populations cannot be controlled or managed well through biosecurity measures or depopulation. This is particularly true of large, mobile marine species like seals. Colonial wildlife, avian and mammalian, may be particularly impacted by influenza A viruses and may allow for ongoing circulation between and within species. This provides opportunity for reassortments of novel strains and mammalian adaptation of virus. Migratory animals may then disseminate virus over broad geographic regions. The wild interface of coastal birds and marine mammals is therefore critical for monitoring influenza A viruses of pandemic potential, particularly in light of the impossibility of replicating such an interface in a research environment.
I'll have a brief postscript after the break.
Outbreak of Highly Pathogenic Avian Influenza H5N1 in New England Seals
Wendy Puryear, Kaitlin Sawatzki, Nichola Hill, Alexa Foss, Jonathon J. Stone, Lynda Doughty, Dominique Walk, Katie Gilbert, Maureen Murray, Elena Cox, Priya Patel, Zak Mertz, Stephanie Ellis, Jennifer Taylor, Deborah Fauquier, Ainsley Smith, Robert A. DiGiovanni Jr., Adriana van de Guchte, Ana Silvia Gonzalez-Reiche, Zain Khalil, Harm van Bakel, V Mia K. Torchetti, Julianna B. Lenoch, Kristina Lantz, Jonathan Runstadler
doi: https://doi.org/10.1101/2022.07.29.501155
This article is a preprint and has not been certified by peer review [what does this mean?].
Preview PDF
Abstract
The recent incursion of Highly Pathogenic Avian Influenza A (H5N1) virus into North America and subsequent dissemination of virus across the continent, has had significant adverse impacts on domestic poultry, and has led to widespread mortality in many wild bird species.
Here we report the recent spillover of H5N1 into marine mammals in the northeastern United States, with associated mortality on a regional scale.This spillover is coincident with a second wave of H5N1 in sympatric wild birds also experiencing regional mortality events.
Viral sequences derived from both seal and avian hosts reveal distinct viral genetic differences between the two waves of infection. Spillover into seals was closely related to virus from the second wave, and one of eight seal-derived sequences had the mammalian adaptation PB2 E627K.
One-Sentence Summary An outbreak of H5N1 in New England seals is the first known population-scale mammalian mortality event associated with the emerging highly pathogenic avian influenza clade 2.3.4.4b.
(Continue . . .)
This recent, rapid spread of HPAI H5 has a lot of scientists genuinely worried (see Nature Why unprecedented bird flu outbreaks sweeping the world are concerning scientists).
Where HPAI H5Nx goes from here is unknowable, but when a virus continually defies expectations, we ignore it at our own peril.
