Cross-species transmission of avian influenza A(H5N1) virus to mammals: lessons learnt from 2024–2025 outbreaks in cattle

Introduction. In 2024–2025, a number of high pathogenicity avian influenza A(H5N1) outbreaks were reported in dairy cattle. Such an expansion of the range of the virus hosts increases global risks for livestock farming and public health, which requires strengthening animal disease monitoring and control systems. Objective. Analysis of the epizootological characteristics of avian influenza A(H5N1) virus infection in dairy cattle and other mammals in 2024–2025, as well as summary of the response measures taken and recommendations of international organizations. Materials and methods. Analytical research methods were used utilizing PubMed, Scopus, Web of Science, Springer, Wiley Online Library databases and materials from international organizations (FAO, EFSA, WOAH, OFFLU, CDC). Results. Outbreaks of avian influenza A(H5N1) caused by clade 2.3.4.4b virus of genotypes B3.13 and D1.1 in dairy cattle in 2024–2025 occurred as a result of three confirmed independent cases of the pathogen transmission from wild birds. The infection was detected on 1,078 cattle farms in 17 US states. Subsequent virus transmission to poultry, wild and domestic animals, including cats, as well as to humans (70 people), mainly those working on animal and poultry farms, was reported. Reverse transmission of the pathogen from cows back to birds was documented as well. Rapid and wide spread of the virus is associated with extensive animal movements and insufficient biosafety measures. Influenza A(H5) is recommended for the inclusion in the differential diagnosis for cattle, pigs, domestic and wild animals. Conclusion. Avian influenza A(H5N1) epizootic in cattle and the infection transmission to other mammals pose a serious threat to livestock production and public health. In response to the existing risks, it is necessary to strengthen biosafety measures and surveillance in epidemiologically significant animal populations, incorporate the experience of other countries and establish international cooperation to study the trends of the virus evolution.