Global health authorities have updated their risk assessment concerning the Avian Influenza A(H3N8) virus, following recent developments in its spread among animals and limited human infections. The joint report from the Food and Agriculture Organization (FAO), the World Health Organization (WHO), and the World Organisation for Animal Health (WOAH) highlights that, despite ongoing animal-to-animal transmission, the overall global public health risk remains low. However, it warns that certain populations, particularly those occupationally exposed to infected animals, face a low to moderate risk of infection depending on the effectiveness of mitigation measures.
Background and Spread
Avian Influenza A(H3N8), a subtype of the broader Influenza A virus family, has been predominantly spread by migratory birds since its resurgence in 2020. The virus has caused widespread deaths among wild bird populations and has triggered outbreaks in poultry across various regions, including Africa, Asia, and Europe. By 2021, it had crossed the Atlantic, reaching the Americas, where it has continued to circulate, with detections in non-avian species, including mammals.
The virus has shown significant genetic diversity, particularly within the clade 2.3.4.4b, which has been responsible for most of the cases reported globally. However, other clades such as 2.3.2.1a and 2.3.2.1c continue to circulate in specific regions, posing additional challenges to global containment efforts.
Human Infections: A Limited But Serious Concern
Since 2021, the WHO has reported 35 human infections caused by the A(H3N8) virus. These cases have primarily been linked to direct or indirect exposure to infected birds or contaminated environments, such as live poultry markets. A few cases have been traced to exposure to infected dairy cattle in the United States, marking a concerning development in the virus’s transmission patterns.
“Although additional human infections associated with exposure to infected animals or contaminated environments are likely to continue to occur, the overall public health impact of such infections at a global level is minor,” the report states. However, it underscores the importance of continuous monitoring, especially given the potential for the virus to undergo mutations that could increase its transmissibility among humans.
The Role of Occupational Exposure
The assessment highlights the particular risks faced by those in close contact with animals, such as farm workers and veterinarians. In affected areas, the risk of infection can range from low to moderate, contingent on the duration and nature of exposure and the consistent use of personal protective equipment.
“The epidemiological situation has changed with the incursion and ongoing spread of A(H3N8) virus in the USA dairy cattle population,” the report notes. As long as the virus continues to circulate in animals and their environments, particularly in unpasteurized milk, further human cases are expected.
Global Health Response and Recommendations
In response to the ongoing threat, the FAO, WHO, and WOAH emphasize the need for a One Health approach, integrating animal, human, and environmental health strategies. The report recommends enhanced surveillance efforts, particularly in detecting the virus in domestic and wild bird populations. It also calls for increased vigilance in monitoring non-avian species that may serve as intermediaries in the virus’s transmission.
Countries are urged to share genetic sequences of the virus and related data in publicly accessible databases to aid in global research and response efforts. The report also stresses the importance of biosecurity measures in preventing the introduction and spread of the virus in livestock, along with good hygiene practices in handling animal products.