Transmission from wild birds and detection in mammals mark a shift in the epidemiological dynamics of highly pathogenic avian influenza (HPAI)
The sustained explosion of highly pathogenic avian influenza (HPAI) viruses, particularly H5 subtypes, is shaping one of the greatest health and ecological challenges of recent decades. Far from being isolated outbreaks, the current situation reflects a panzootic that, since 2021, has affected multiple continents, broadening its host range and generating unprecedented consequences for biodiversity, animal health, and human health alike.
The most recent data from international bodies point to persistent viral circulation, with increasingly intense seasonal peaks and growing epidemiological complexity. Between late 2025 and early 2026, Europe reported more than 2,500 detections of HPAI A(H5) viruses, of which more than 80% were in wild birds, confirming the central role of these reservoirs in transmission dynamics.
A shift in epidemiological patterns
Traditionally associated with poultry and wild waterfowl, avian influenza has undergone a significant behavioural change in recent years. Subtype A(H5N1), in particular, has broadened its host spectrum, as reported by the World Organisation for Animal Health (OMSA), with more than 50 mammal species affected globally. This phenomenon reflects the virus’s increased adaptive capacity and raises questions about its future evolution.
Subtype A(H5N1), in particular, has broadened its host spectrum, as reported by the OMSA, with more than 50 mammal species affected globally
In Europe, according to the European Food Safety Authority (EFSA), during the winter of 2025–2026, more than 90% of poultry outbreaks were associated with introductions from wild birds, underscoring the difficulty of controlling the disease through farm-level measures alone. Furthermore, wild waterfowl recorded higher levels of impact than in previous seasons, consolidating their role as key vectors.
At the global level, the situation is equally concerning. In North America, the virus remains widely distributed in wildlife, while in remote regions such as the sub-Antarctic islands, very severe impacts have been documented. Particularly notable is the case of southern elephant seals, with losses of up to 50% of breeding females in some territories, as well as recurrent outbreaks in colonies of iconic seabirds such as albatrosses.
A threat to biodiversity
One of the most alarming aspects of the current panzootic is its impact on biodiversity. High mortality in wild species, combined with reproductive failure and disruption of population dynamics, is generating profound ecological disturbances.
The collapse of local populations, such as those recorded in certain migratory bird species, not only jeopardises their conservation but may also trigger cascading effects on ecosystems. The disruption of trophic networks, the loss of ecosystem services, and the modification of interspecific interactions are among the consequences identified by experts.
Moreover, the persistence of the virus in the environment, facilitated by factors such as the concentration of birds in wetlands or the presence of artificial feeding points, contributes to maintaining infection pressure and hampering the recovery of affected populations.
Emerging risks within the One Health framework
The expansion of avian influenza beyond birds introduces new concerns within the One Health framework. The growing detection of the virus in mammals (including wild carnivores and, potentially, livestock) increases the risk of viral adaptation and the emergence of variants with greater transmission capacity.
In this regard, one of the most significant findings of the latest surveillance period in Europe has been the possible transmission from wild birds to dairy cattle in the Netherlands, an event that could have significant implications for animal health and agri-food production should the situation worsen.
In humans, although the risk to the general population remains low, sporadic cases have been reported, mainly associated with direct exposure to infected birds or contaminated environments. Between late 2025 and early 2026, ten human infections were recorded in Asia, with no fatal cases and no evidence of person-to-person transmission. In addition, at the end of March, Italian health authorities confirmed the detection of the first human case of avian influenza A(H9N2) in the European Union, in a patient who had recently travelled to a non-European country where this virus circulates in birds.
Nevertheless, health authorities warn that the high level of viral circulation increases the likelihood of exposure, particularly among professional groups such as poultry workers, veterinarians, and staff at wildlife rehabilitation centres.
It is worth noting that, from 10 February 2026, the whole of Spanish territory regained its disease-free status in accordance with the provisions of the OMSA code.
Biosecurity and surveillance: the pillars of control
In this context, biosecurity remains the primary tool for preventing the introduction and spread of the virus on poultry farms. The highly contagious nature of the disease, in both its highly pathogenic and low pathogenic forms, demands the strict application of control measures, including limiting contact with wild birds, disinfecting facilities, and controlling movements.
Epidemiological surveillance, in both domestic and wild birds, is equally crucial. Early outbreak detection, combined with genomic characterisation of viruses, makes it possible to identify changes in their behaviour and anticipate potential risks.
Likewise, the exchange of information between countries and sectors — health, veterinary, and environmental — is considered essential for a coordinated and effective response.
Beyond traditional measures, international experts advocate the implementation of innovative approaches to strengthen ecosystem resilience and reduce pathogen transmission. These include nature-based solutions such as wetland restoration, coastal habitat protection, and the promotion of scavenger species populations that contribute to the removal of infected carcasses.
These strategies seek not only to mitigate the impact of avian influenza, but also to address other factors that favour the spread of disease, such as biodiversity loss, climate change, and ecosystem degradation, all of which highlight the interconnection between animal, human, and environmental health, and the need for integrated and sustained responses over time. The scale of the impacts observed to date suggests that the consequences could extend across generations, particularly with regard to biodiversity.
A global challenge
The current avian influenza panzootic highlights the interconnection between animal, human, and environmental health, and the need for integrated and sustained responses over time. The scale of the impacts observed to date suggests that the consequences could extend across generations, particularly with regard to biodiversity.
Although the risk to public health remains limited at present, the evolution of the virus and its capacity to adapt to new hosts make constant vigilance essential. In a context of increasing pressure on ecosystems, avian influenza is becoming established as an indicator of emerging challenges in global health and a reminder of the importance of adopting a truly multidisciplinary approach.
Source:
-. Gazeta Médica (Andrea Rivero García), 6-4-26
For further information:
-. Avian Influenza on NeXusAvicultura