Influenza A in Birds: The Reservoir That Never Dies Out

Birds are not merely victims of major avian influenza epizootics. They are the natural reservoir for these influenza viruses and, above all, the primary driver of their evolution. As one article points out: as long as influenza viruses of type A circulate among birds, the risk of new outbreaks will remain inherent. In wild species, particularly ducks and geese, infection is most often asymptomatic. The viruses circulate without causing any apparent disease, carried by large-scale migrations. This discreet circulation promotes considerable genetic diversity. The segmented genome of influenza A allows not only for frequent mutations but also for the exchange of segments between influenza viruses (reassortment), giving rise to new lineages. When these viruses jump from wild birds to domestic poultry, the balance shifts dramatically. On poultry farms, certain strains—particularly H5 and H7—can evolve into highly pathogenic forms, causing massive mortality and large-scale culls. Since the early 2020s, this dynamic has no longer been limited to seasonal outbreaks: avian influenza has become a long-term phenomenon, circulating almost continuously in Europe and elsewhere. The risk to humans remains low, but it cannot be ruled out. The danger a virus poses to birds does not determine its zoonotic potential. On the other hand, the more a virus circulates and multiplies, the greater the opportunities for adaptation. The history of influenza pandemics reminds us that cross-species transmission is rare, but never accidental. Faced with this reality, the authors are under no illusions: eradication is out of reach. The wild avian reservoir cannot be eliminated. The response therefore rests on a now well-established three-pronged approach: surveillance, biosecurity, and, increasingly, poultry vaccination. The latter is gaining ground but raises technical, economic, and commercial questions, particularly regarding the traceability of vaccinated animals. Avian influenza is not an anomaly in the system. It is the product of an ancient, stable, and deeply rooted viral ecology. The real question is not whether new viruses will emerge, but whether surveillance systems will be able to detect them early enough to prevent them from reaching a new scale.