In recent years, highly pathogenic avian influenza (HPAI) has transformed from a seasonal phenomenon associated with migratory birds in specific regions to a constant global risk. The influenza virus, which has long plagued the poultry industry, is now also increasingly recognized as a potential public health issue.
Previously, Europe experienced HPAI epidemics as a seasonal event, with migratory waterfowl spreading the virus during their autumn return to overwintering sites.
However, since 2020, the situation has changed significantly. HPAI viruses, particularly the influenza A(H5) subtype, are causing the worst bird epidemics to date. Over 14,000 outbreaks have been reported, with approximately 96 million farmed birds culled in Europe alone.
In an editorial published in Eurosurveillance, Cornelia Adlhoch of the European Centre for Disease Prevention and Control (ECDC) and Francesca Baldinelli of the European Food Safety Authority (EFSA) analyze the rapid development and geographical extension of HPAI in recent years. They reveal that the virus has moved away from seasonality, spreading from west to east along migratory bird routes towards Southeast Asia.
Furthermore, the A(H5N1) virus has spread from Europe to North America for the first time, rapidly progressing across large areas of Canada and the United States (US). Similarly, a north to south spread during autumn bird migration has been observed, reaching as far as the southern tip of Chile.
Although the current risk to human health is limited, the experts warn that the introduction of avian influenza viruses into mammalian populations could increase the risk of influenza virus reassortment, leading to adaptation and spread among mammals. “With the ongoing global presence of A(H5) HPAI viruses, further sporadic spill-over events to humans cannot be excluded,” said the researchers.
The rapid spread of the A(H5N1) virus to previously unaffected areas and its successful persistence during summer months has likely been facilitated by ongoing evolution and reassortment with local low pathogenic avian (LPAI) viruses. This has led to the adaptation of HPAI viruses to new or previously rarely affected wild bird species, such as barnacle geese or sea birds.
Consequently, HPAI viruses have impacted wild bird populations worldwide, with the influenza A(H5N1) virus causing the death of more than 40 percent of the pelican population in Chile and Peru.
The experts also refer to global reports of HPAI transmission to mammals like minks and sea lions, which increases the risk of the virus spilling over to pet animals through contact with dead or sick wild birds or mammals such as foxes.
While human infections with A(H5N1) have been reported in a few countries, symptoms vary from mild to severe, and even death, often related to exposure to infected birds, culling activities, or contaminated environments.
“Although currently circulating avian influenza viruses retain a preference for avian-type receptors, different mutations associated with transmission to and pathogenicity in mammals have been observed,” said the researchers. “These mutations were detected sporadically in infected wild and domestic birds and more often emerged upon transmission events to mammals.”
To address the threat of avian influenza, the authors advocate for a One Health approach, which entails rapid sharing of outbreak information, provision of sequence data and reference viruses, and close collaboration between different sectors both locally and globally.
Communication campaigns may help increase public awareness and recognition of avian influenza as a threat to animal and human health, reducing the risk of contact with potentially infected animals.
There are many types of avian influenza viruses, but only a few of them have caused serious concerns for human health, most notably H5N1, H7N9 and H5N8. These viruses can be deadly to domestic birds, such as chickens, ducks, and turkeys.
Transmission of bird flu viruses to humans is relatively rare and usually requires direct or close contact with infected birds, or heavily contaminated environments. The disease is not typically transmitted from person to person, but there have been instances of limited transmission between humans, often in circumstances where there was close and prolonged contact.
In humans, avian influenza can cause severe disease, including pneumonia, acute respiratory distress syndrome, and even death. The symptoms can range from typical influenza-like symptoms (fever, cough, sore throat, and muscle aches) to severe respiratory illness and other complications.
Public health organizations closely monitor avian influenza outbreaks in birds and humans because of the potential for the virus to mutate and gain the capability to spread easily among humans, which could lead to a pandemic. As of now, no avian influenza virus has gained the ability to spread easily among humans.
Prevention strategies include close monitoring and culling of infected birds, and the use of influenza vaccines in high-risk populations.
It is also recommended that people avoid contact with domestic birds in areas where there is known avian influenza, and practice good hand hygiene to reduce the risk of infection. There is ongoing research into developing more effective vaccines and treatments for avian influenza.