#18,867
In the 4 years HPAI H5N1 began its latest global diaspora, we've witnessed an incredible increase in both its geographic, and host, ranges. The virus has since conquered both North and South America, has encroached into the Antarctic, and now threatens Australasian.
Huge populations of marine mammals have been killed, > 1000 dairy herds have been infected, and uncounted thousands of other mammals have died (see also Nature Reviews: The Threat of Avian Influenza H5N1 Looms Over Global Biodiversity).Spillovers into mammals - once relatively rare - have become both commonplace and constant; often with devastating neurological impacts.
These milestones have become so common, that events that would have inspired screaming headlines 2 years ago are scarcely noticed today (see Avian Flu's New Normal: When the Extraordinary Becomes Ordinary).
Today we've a brief update in Influenza & Other Respiratory Viruses that reports - in a climate of reduced surveillance and testing - a nearly 50% increase in the number of mammalian species infected by H5Nx over the past year.
I've only posted some excerpts. Follow the link to read it in its entirety.
Update on H5N1 Panzootic: Infected Mammal Species Increase by Almost 50% in Just Over a Year
Pablo Plaza, Sergio A. Lambertucci
First published: 10 September 2025
https://doi.org/10.1111/irv.70159
Funding: This work is supported by the Agencia Nacional de Promoción Científica y Tecnológica (PICT-2018-1623 and PICT-2021-TI-00039) and Universidad Nacional del Comahue (project 04/B260).
The current panzootic caused by the highly pathogenic avian influenza virus A(H5N1) (hereafter, H5N1) is having devastating effects on animal and ecosystem health; the virus has spread globally, causing alarming mortalities in a wide range of domestic and wild animals [1]. By early 2024, at least 50 mammal species had been reported infected by H5N1, with massive mortalities in some cases; viral mutations suggest the virus is adapting to infect mammals [2].This epidemiological situation puts humans at risk due to the potential emergence of a new viral variant capable of triggering a new pandemic. Here, we provide a global update on mammals infected by H5N1 up to July 2025 following the methodology previously used by Plaza et al. [2], which is based on a search of scientific literature and diverse global databases.
1 Mammal Species Infected
We found that between March 2024 and July 2025, 24 new species were recorded as infected, representing almost a 50% increase in the number of species (Figure 1A,B). The current 74 mammalian species known to be infected by this virus include domestic, synanthropic (i.e., wild species that live in human-modified environments and obtain benefits from humans), and wild species (Figure 1A). Humans use some o these species for productive purposes, such as breeding or harvesting for fur and food (Figure 1A), and several may act as mixing vessels (Figure 1A). Even considering the figures are underestimations [1], the Mustelidae family is the most affected (more than 50,000 cases, mostly in captivity for fur production), followed by the families Otariidae (> 24,000 cases, in the wild), Phocidae (> 18,000 cases, in the wild), Canidae (> 11,000 cases, mostly in captivity for fur production), and Bovidae (> 1000 cases, in dairy production) (Figure 1A).
FIGURE 1
(A) Phylogenetic tree of mammalian species reported as infected by H5N1. The color of the species names represents the number of reported cases in the literature and databases. Colored dots indicate whether a species is domestic or synanthropic, used for human production, a potential mixing vessel, or meets all these criteria. (B) Number of species infected from 2020 to March 2024 and from March 2024 up to July 2025. (C) Percentage of species categorized as domestic or synanthropic, used for human production, or considered potential mixing vessels (bubble size represents the percentage magnitude). DS, domestic or synanthropic; HP, used for human production; MV/DS, domestic or synanthropic and potential mixing vessels; MV, potential mixing vessels. See main text for how the data presented in this figure were obtained.
(SNIP)
2 Concluding Remarks
The number of mammalian species infected by this zoonotic pathogen and the number of cases are rapidly increasing (Figure 1A,B). Although increased testing may have influenced this result, the almost 50% rise in species in just over a year is highly concerning. Some species pose a significant risk to humans due to their large populations, close proximity to human settlements, and potential role as mixing vessels.
Surveillance for high-risk species (i.e., mixing vessels with large populations living near humans) should be a global priority. The lack of information about the H5N1 epidemiological situation in some regions (e.g., some areas of the Global South) should be addressed by promoting surveillance programs and providing funds and technology [1].
The most affected mammalian species are those used by humans, particularly in intensive production systems. This makes management of the H5N1 spread challenging because the virus is strongly associated with our unsustainable ways of living and production methods [6]. If this panzootic is not addressed from a holistic, ecological, productive, and interdisciplinary perspective, only palliative action will be possible, with a limited effect in reducing the negative impact of this pathogen. H5N1 is already spread globally—not only in birds but also in mammals; it is time to put all our effort into reducing its impacts on wild and domestic species but also its spread to humans.
Despite its unprecedented global spread, and its increased (mammalian and avian) host range, we continue to treat HPAI H5Nx as if it is the same virus that failed to spark a pandemic in 2006-2008.
Even if HPAI H5 fails to ever spark a human pandemic, its impact on our shared ecosystem is enormous, and continues to grow.
While I can't tell you what negative impacts the loss of a Billion+ wild birds, or a quarter of a million marine mammals - or unfathomable numbers of peridomestic mammals - might have on our society, one thing is certain.
We are well on our way to finding out.
