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Our study identified strains of the A/H5N1 virus in analyzed samples of subsistence poultry, wild birds, and mammals, belonging to clade 2.3.4.4b, genotype B3.2, with very high genetic similarity to strains from Chile, Uruguay, and Argentina. This suggests a migratory route for wild birds across the Pacific, explaining the phylogenetic relatedness. The Brazilian samples displayed similarity to strains that had already been previously detected in South America. Phylogeographic analysis suggests transmission of US viruses from Europe and Asia, co-circulating with other lineages in the American continent. As mutations can influence virulence and host specificity, genomic surveillance is essential to detect those changes, especially in critical regions, such as hot spots in the HA, NA, and PB2 sequences. Mutations in the PB2 gene (D701N and Q591K) associated with adaptation and transmission in mammals were detected suggesting a potential zoonotic risk. Nonetheless, resistance to neuraminidase inhibitors (NAIs) was not identified, however, continued surveillance is crucial to detect potential resistance. Our study also mapped the spread of the virus in the Southern hemisphere, identifying possible entry routes and highlighting the importance of surveillance to prevent outbreaks and protect both human and animal populations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

In 2021, the H5N1 virus lineage 2.3.4.4b spread to the Americas, causing high mortality in wild and domestic avian populations. South American countries along the Pacific migratory route have reported wild bird deaths due to A/H5Nx virus since October 2022. However, limited genomic data resulted in no cases reported in Brazil until May 2023. Brazil reported its first case of highly pathogenic avian influenza virus (HPAI A/H5N1) in May 2023. The virus was detected in Cabot's tern specimen in Marataízes, Espírito Santo. Cases were also found in backyard poultry and other wild birds, but no human or commercial poultry cases occurred. HPAI poses risks to the poultry industry, food security, and public health. Researchers used next-gen sequencing and phylogenetic analysis to study the Brazilian sample. It confirmed its affiliation with the 2.3.4.4b clade and proximity to sequences from Chile and Peru. This sheds light on the spread and evolution of HPAI A/H5N1 in the Americas, emphasizing continuous monitoring to mitigate risks for both avian and human populations. Understanding the virus's genetics and transmission allows implementing effective control measures to protect public health and the poultry industry., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 Ministry of Agriculture Husbandry. Published by Elsevier Ltd.)