Italian
The H5N1 epidemic affects millions of wild birds and spreads among different species, threatening global biodiversity and ecosystems
Last week, while working at a veterinary clinic in Auckland, I witnessed a seemingly mundane yet revealing scene of the historical moment we are living in. An injured seagull had been urgently brought in by the public, and the on-duty veterinarian, after assessing its precarious health, immediately contacted the MPI — the Ministry for Primary Industries, the New Zealand government agency responsible for biosecurity, food safety, and animal disease management. What puzzled the veterinarian was the healthy appearance of the seagull and what seemed like a sudden decline in its respiratory system.
The question, for those not immersed in the veterinary world, arises spontaneously: why should the government of New Zealand be interested in the corpse of a common wild bird? The answer is that highly pathogenic avian influenza, known as H5N1, has become the most severe animal epidemic ever recorded. In just a few years, it has transformed a virus once confined to poultry farms into a global threat to wildlife and, potentially, to public health. What is happening is unprecedented in the recent history of infectious diseases.
Traditionally, HPAI was considered a livestock issue: an aggressive pathogen, yes, but almost exclusively related to poultry. Wild bird populations, while sometimes able to become infected, did not serve as a driver of spread. This time, however, something completely different has happened. The H5N1 variant that emerged around 2020 has acquired the ability to establish itself in migratory birds and in colonies of seabirds, transforming into an unwanted passenger on the major global migratory routes.
From that moment on, its expansion became unstoppable: Europe, Africa, Asia, the Americas, and even Antarctica, where the spread among penguins and seals poses a huge ecological risk for species that have no adaptive defense against this type of virus.
The effects are measured in millions of dead animals, but the actual estimates are likely much higher: many carcasses disappear at sea or in remote areas not reached by monitoring. Colonial species — such as gannets, gulls, terns, and albatrosses — are the most vulnerable because they live and nest closely together, facilitating explosive transmission. Raptors have also been hit hard, infected by contaminated prey: the bald eagle in the United States, the California condor, hawks, owls, and kites in many parts of the world.
The loss of so many predators, scavengers, and seabirds will have repercussions on ecosystems for years, perhaps decades.
To further complicate the situation, in recent months the virus has begun to circulate among dairy cattle as well. This has never happened on this scale before. Affected cows may show a decrease in milk production, fever, and respiratory symptoms, but the real problem is that the virus is demonstrating an unexpected biological flexibility. Each new animal reservoir represents an additional opportunity for the virus to change, adapt, and enhance its transmission capabilities.
So far, human infections have been very few, all linked to very close contact with infected animals or contaminated environments — such as poultry farms or, more recently, herds of cattle. However, the mortality observed in the human cases recorded so far has been extremely high. There is currently no evidence of sustained person-to-person transmission, and this is what keeps the overall risk low.
The fear of epidemiologists, however, is clear: that the virus may acquire, through repeated attempts, the necessary mutations to spread efficiently among people, as happened with the virus of the 1918 pandemic or, more recently, with SARS-CoV-2
The main defense remains prevention. Health authorities recommend avoiding contact with sick or dead birds and promptly reporting any suspicious findings to dedicated hotlines — such as the Emergency Animal Disease Hotline in Australia — or through citizen science applications, like BirdTrack in the UK.
Although the risk to the general population remains low for now, the situation requires constant monitoring: H5N1 is one of the deadliest viruses ever identified, and its massive spread in wildlife creates an unpredictable evolutionary environment.
The H5N1 epidemic is not just a story of sick animals: it is an emblematic case of how fragile the balances are between nature, farming, and public health. Virginie Courtier, a French virologist, has called it “the greatest crisis for wild birds in recent centuries.”
With the virus continuing to move between different species, from birds to marine mammals to cows, it is becoming increasingly clear that the protection of biodiversity and human health are deeply interconnected.
