A highly pathogenic avian influenza A(H5N1) virus of clade 2.3.4.4b was identified as the cause of an epizootic in dairy cattle on a single farm in Texas, USA, during March and April 2024. The study used molecular, cell culture, and next-generation sequencing techniques to confirm the presence of the virus in 40 swab specimens from 30 cows, with 24 sick and 6 healthy. The virus was detected only in sick cows, and no other viral families were found to be co-infecting. The virus was more prevalent in nasal swabs than rectal swabs, suggesting respiratory tract involvement in cow-to-cow transmission. The study also found that one sick cow had evidence of bovine viral diarrhea virus (BVDV), but the presence of BVDV in healthy cows suggests it may not be the cause of the unusual illness. The complete genome of the H5N1 virus isolated from a sick cow was found to be very similar to H5N1 strains from dead birds, other cattle, and a cattle worker, indicating a possible single interconnected multispecies outbreak in Texas. The study highlights the importance of interdisciplinary cooperation under a One Health framework to address complex epizootic events. The findings emphasize the need for further research to understand the pathogenicity of these viruses and to develop strategies for preventing future outbreaks. The study also acknowledges the limitations of the research, including the lack of data on milk, animal workers, and environmental specimens. The research was supported by various funding sources, and the data are available for further study.A highly pathogenic avian influenza A(H5N1) virus of clade 2.3.4.4b was identified as the cause of an epizootic in dairy cattle on a single farm in Texas, USA, during March and April 2024. The study used molecular, cell culture, and next-generation sequencing techniques to confirm the presence of the virus in 40 swab specimens from 30 cows, with 24 sick and 6 healthy. The virus was detected only in sick cows, and no other viral families were found to be co-infecting. The virus was more prevalent in nasal swabs than rectal swabs, suggesting respiratory tract involvement in cow-to-cow transmission. The study also found that one sick cow had evidence of bovine viral diarrhea virus (BVDV), but the presence of BVDV in healthy cows suggests it may not be the cause of the unusual illness. The complete genome of the H5N1 virus isolated from a sick cow was found to be very similar to H5N1 strains from dead birds, other cattle, and a cattle worker, indicating a possible single interconnected multispecies outbreak in Texas. The study highlights the importance of interdisciplinary cooperation under a One Health framework to address complex epizootic events. The findings emphasize the need for further research to understand the pathogenicity of these viruses and to develop strategies for preventing future outbreaks. The study also acknowledges the limitations of the research, including the lack of data on milk, animal workers, and environmental specimens. The research was supported by various funding sources, and the data are available for further study.