#18,595
Last month we looked at a paper (see Nature Reviews: The Threat of Avian Influenza H5N1 Looms Over Global Biodiversity) published by Sergio A. Lambertucci, Andrea Santangeli & Pablo I. Plaza on the growing impact of HPAI H5 on our global biosphere.
While numbers are impossible to quantify, hundreds of millions of wild and farmed birds have died, and hundreds of thousands - perhaps millions - of wild mammals have succumbed to the virus (see Travel Med. & Inf. Dis.: Pacific and Atlantic Sea Lion Mortality Caused by HPAI A(H5N1) in South America).
Last year, for the very first time, we witnessed large-scale spillovers into farmed animals (dairy cows, alpacas, goats, and even a couple of pigs). Even household pets - primarily cats - have been affected (see Emerg. Microbes & Inf.: Marked Neurotropism and Potential Adaptation of H5N1 Clade 2.3.4.4.b Virus in Naturally Infected Domestic Cats).
HPAI H5 viruses have become entrenched in the environment (see Environmental Surveillance and Detection of Infectious HPAI Virus in Iowa Wetlands) and are spreading in ways we only partially understand (see Osterholm Podcast: The Potential Environmental (Airborne) Spread of H5N1).
While sustained human-to-human transmission has not been detected - and many recent human cases have been uncharacteristically mild - by just about every other metric, alarm bells are ringing in the scientific community.
There is an old saying among epidemiologists; “If you’ve seen one pandemic . . . you’ve seen one pandemic.”
Which is why the (comparatively mild) pandemics of 1957 (H2N2), 1968 (H3N2), and 2009 (H1N1) left us unprepared for the millions of deaths we saw due to COVID. Even after the events of the last 5 years, many still refuse to accept the possibility that that there could be something even worse in our future.
All of which brings us to a brief overview (once again penned by Plaza & Lambertucci) on the differences between the last two pandemics, and the current threat posed by H5N1. I've only posted a few excerpts below, so follow the link to read it in its entirety.
I'll have a brief postscript after the break.
Differences between Influenza H5N1, A/H1N1 2009, and SARS-CoV-2 in a pandemic risk scenario
Pablo I. Plaza, Sergio A. Lambertucci
Under a Creative Commons license
In under two decades, we have suffered two pandemics caused by viruses emerging from animals, namely the A/H1N1 2009 virus and SARS-CoV-2, which resulted in large human fatalities [1], [2]. Currently, another zoonotic pathogen, the Highly Pathogenic Avian Influenza virus A(H5N1) (hereafter, H5N1), is threatening humans with a new pandemic. Since late 2020, this pathogen has modified its epidemiology, shifting from infecting mainly domestic birds to severely affecting wild birds and mammals [3]. H5N1 has also affected humans: at least 900 human cases were reported from 2003 to December 2024 [4], [5]. Human-to-human transmission, however, has not been reported [5]. This pathogen genomic now favors mammalian infection, even in domestic species intended for human consumption [5]. Consequently, the risk of human-to-human transmission that could provoke a pandemic warrants serious consideration by governments, public health authorities and society [4].
The global consequences of H5N1 in wild and domestic animal species—and potentially in humans should it continue to adapt —may be even greater and more challenging to manage than those caused by A/H1N1 in 2009 and SARS-CoV-2. Unlike these pathogens, which primarily affected the human health sphere of the One Health approach, H5N1 currently affects the animal and ecosystem health spheres, putting human health at risk (Fig. 1). Moreover, in the absence of contingency plans, the implications for human health could exceed those of A/H1N1 2009 and SARS-CoV-2.
Compared with the A/H1N1 2009 and SARS-CoV-2, H5N1 poses additional threats to the human health sphere by impacting food security and safety. Animals intended for human consumption, particularly poultry and cattle, are being severely affected by H5N1 [3], [5], with catastrophic consequences for the food industry, especially poultry. This usually affects the availability and price of animal products (e.g., eggs and chicken meat, or cow milk), affecting access to these essential food sources. This effect was not reported during the A/H1N1 2009 or SARS-CoV-2 pandemics. The A/H1N1 2009 virus was not associated with a significant impact on food security [2], [7], and SARS-CoV-2 only moderately affected some aspects of this issue, especially in low-income countries [1]. One disquieting aspect of H5N1 is that food of animal origin could be a source of infection for humans if not handled and cooked properly, presenting an additional risk of infection [5].The emergence of a new pandemic risk so soon after the A/H1N1 2009 and SARS-CoV-2 pandemics indicates that insufficient measures have been taken to reduce the emergence of pathogens that threaten One Health. A global contingency plan—including vaccines, antiviral treatments, and medical infrastructure—is essential to prepare for potential human–to–human transmission of H5N1. Urgent action is required to mitigate the negative impact of H5N1 on the animal and ecosystem health spheres if we are to reduce its ecological impact and the risk to human health.
HPAI H5 isn't the only pandemic threat out there, but right now it is making moves that are hard to ignore. Perhaps we'll get lucky, and discover there is some species barrier that prevents it from spreading efficiently among humans, but that doesn't mean the threat vanishes.
H5Nx could still reassort with a seasonal flu virus, potentially creating a more virulent H1 or H3 virus. Or we could get blindsided by an avian H10 or H7 virus from out of left field. Or maybe another SARS-like virus.
But even if none of that happens, the impact of H5Nx on global wildlife, on the food supply, and on local economies, could have a tremendous impact.
Who knows what the loss of a billion birds will do to our ecosystem? Or the deaths of tens of thousands of marine mammals. Or the continued spread of HPAI H5 to other farmed animals?
While many choose to ignore these possibilities, we appear inexorably on the path of finding out.