#18,005
Although HPAI H5 has been a pandemic concern for most of the past 2 decades, it is safe to say that the abrupt changes in the virus's behavior over the past 2-3 years have raised the stakes significantly.
Since 2021 we've see increased spillover into mammalian species (see graphic above), with many displaying severe neurological symptoms.
Travel Med. & Inf. Dis.: Pacific and Atlantic Sea Lion Mortality Caused by HPAI A(H5N1) in South America
J. Virulence: HPAI H5N1 Virus Infection In Companion Animals
EID Journal: HPAI A(H5N1) Virus Clade 2.3.4.4b Infections in Wild Terrestrial Mammals, United States, 2022
Cell: The Neuropathogenesis of HPAI H5Nx Viruses in Mammalian Species Including Humans
In addition to poultry and wildlife, farmed animals - including mink, foxes, pigs and most recently goats and dairy cows - have all been affected by the virus. How widespread these spillovers really are is unknown, but they are likely far more common than has been reported.
Surveillance and testing is limited, even in places like the United States and Europe, while in many regions of the world, surveillance is practically non-existent. Some countries - for economic or political reasons - may know of outbreaks, but may be reluctant to share that information (see Flying Blind In The Viral Storm).
But even with the limited dataset we have, it is pretty obvious that the behavior of HPAI has changed over the past 3 years. Where, exactly, all of this will lead is unknown. But we need to be prepared for more - potentially unpleasant - surprises in the future.
Assumptions about how this virus behaves, and the threat it poses going forward, may need to be adjusted. As may many of our current health and safety practices (see examples below).
UK Guidance for the Public: Minimize Contact with Wild Birds
Two days ago, in AJVR: The Virus is Out of the Barn: The Emergence of HPAI, we looked at a cautionary report from the American Journal of Veterinary Research, which goes into the history of HPAI (and LPAI) viruses, and examines the risks posed by increasing spillovers into mammalian species (including pigs).
Today we've a report from another prestigious veterinary journal (JAVMA - Journal of the American Veterinary Medical Association), that describes the evolution - and unprecedented changes in behavior - of HPAI over the past 3 years.
This is a lengthy, and highly informative, review and is well worth reading in its entirety. I'll have a brief postscript after the break.
High-pathogenicity avian influenza in wildlife: a changing disease dynamic that is expanding in wild birds and having an increasing impact on a growing number of mammals
Wendy B. Puryear PhD and Jonathan A. Runstadler
DVM, PhD jonathan.runstadler@tufts.eduView More
DOI: https://doi.org/10.2460/javma.24.01.0053
Volume/Issue: Online Early
Online Publication Date: 10 Apr 2024
Abstract
While diverse strains of low-pathogenicity avian influenza have circulated in wild birds for a long period of time, there has previously been little pathology in wild birds, ducks have been the primary and largely asymptomatic wild reservoir, and spillover into mammals has been limited and rare.
In recent years, a high-pathogenicity avian influenza (HPAI) virus has emerged on the global scene and shifted the previously established dogmas for influenza infection. High-pathogenicity avian influenza has expanded into wildlife in unprecedented numbers and species diversity, with unmatched disease severity for influenza in wildlife.
As the disease ecology of influenza has shifted with this new variant, significant efforts are underway to understand disease course, pathology, and species susceptibility. Here we focus primarily on the impact that HPAI has had in wild mammals while framing these novel spillovers within the context of significantly expanding disease in avian species and geography. The clinical and pathology presentations of HPAI in these atypical hosts are discussed, as well as prognosis and risk for continued spillover.
The companion Currents in One Health by Runstadler and Puryear, AJVR, May 2024, provides further context on viral reservoirs and possible routes of direct or environmental transmission and risk assessment of viral variants that are emerging within wildlife.
(SNIP)
Conclusions
After the initial incursion of Eurasian-origin H5N1 2.3.4.4 virus into North America from trans-Atlantic migratory birds,46 there have continued to be additional incursions of new lineages.25,47,48 These have occurred primarily from Europe,47 across Iceland,49 and onto the North Atlantic seaboard.25 Incursions of HPAI have also been observed from the Pacific.25 In addition to an ongoing influx of new lineages, HPAI continues to reassort and evolve.38,48 The spillover into mink in Spain was associated with an H5N1 reassortment with a gull-associated LPAI H13 variant.23 A gull-adapted reassortment termed the BB genotype has become common in Europe and is responsible for the fur farm outbreaks in Finland43 but is as yet undetected in North America. The HPAI reassortment H5N5 has recently been detected in North America, entering along the trans-Atlantic route, and associated with mortality in raccoon, red fox, and striped skunk in Canada.15
The current HPAI outbreak is unique in global expansion and in the wildlife species diversity that it is impacting and the range of wild mammals in which it is being detected. In March of 2024, infection of several dairy herds in multiple states was diagnosed, with possible transmission to a second human case in the US.50–52
Though the risk to humans remains low, this unexpected outbreak well illustrates the continued need for vigilance and further study. As the range of HPAI expands and the frequency of mammalian infections increase, the risk of zoonotic transmission continues to increase. This is why it is critical that robust surveillance occurs and appropriate biosafety caution is exercised, particularly in novel and atypical hosts, so that evidence for mammalian adaptation and mammal-to-mammal spread can be captured as early as possible. This then allows for variants to undergo pandemic risk assessment and to help inform vaccine preparedness efforts, as detailed further in the companion Currents in One Health article by Runstadler and Puryear, AJVR, May 2024.
Although it remains to be seen whether HPAI H5 has what it takes to spark a pandemic, there is almost certainly another pandemic in our future. While an influenza virus is the most likely culprit, another coronavirus, or perhaps something far afield (aka `Disease X') is always possible.
Many scientists believe the frequency of pandemics and epidemics will only increase in the future (see BMJ Global: Historical Trends Demonstrate a Pattern of Increasingly Frequent & Severe Zoonotic Spillover Events).
Given the risks - and our bitter experience with COVID - it makes sense to be preparing with some urgency for whatever comes down the pike next. The following quote is 18 years old, but it is just as true today as it was in 2006:
“Everything you say in advance of a pandemic seems alarmist. Anything you’ve done after it starts is inadequate." - Michael Leavitt, Former Secretary of HHS
