Update on H5N1 Panzootic: Infected Mammal Species Increase by Almost 50% in Just Over a Year

Abstract

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.

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 of 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).

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.

Pablo Plaza: conceptualization, data curation, investigation, writing – original draft, writing – review and editing, methodology, funding acquisition. Sergio A. Lambertucci: conceptualization, methodology, data curation, investigation, project administration, funding acquisition, writing – original draft, writing – review and editing, supervision.

The authors have nothing to report.

The authors have nothing to report.