A highly pathogenic avian influenza A (H5N1) virus belonging to clade 2.3.4.4b was detected in dairy cattle and domestic cats in Texas, USA, in March 2024. This virus, which had not previously been reported in domestic cattle, showed a sudden drop in milk production and shared nearly identical genome sequences, forming a new genotype B3.13 within the 2.3.4.4b clade. The virus underwent two reassortment events since 2023 and exhibited critical mutations in HA, M1, and NS genes, but lacked critical mutations in PB2 and PB1 genes that enhance virulence or adaptation to mammals. A human case with the PB2 E627K mutation was identified, highlighting the potential for rapid evolution post-infection. The virus was detected in dairy cattle, domestic cats, and wild birds in Texas, and confirmed by the National Veterinary Service Laboratories. Genomic analysis revealed that the virus is a reassortant of genotype B3.7 and a low pathogenic avian influenza virus. The virus showed high nucleotide identity in its genome sequences, forming a distinct phylogenetic subcluster. The detection of the virus in bovine milk raises public health concerns related to zoonotic transmission through unpasteurized milk. The virus was also detected in dairy herds in Idaho, Michigan, Ohio, North Carolina, and South Dakota, and in a human case after contact with infected dairy cattle. The virus's ability to spread through migratory birds and global trade networks has led to its dissemination across multiple continents. The virus's potential for adaptation to mammalian hosts and its ability to evolve rapidly pose significant public health risks. The study highlights the need for continued surveillance and monitoring to assess the virus's impact on human health and to develop strategies for prevention and control.A highly pathogenic avian influenza A (H5N1) virus belonging to clade 2.3.4.4b was detected in dairy cattle and domestic cats in Texas, USA, in March 2024. This virus, which had not previously been reported in domestic cattle, showed a sudden drop in milk production and shared nearly identical genome sequences, forming a new genotype B3.13 within the 2.3.4.4b clade. The virus underwent two reassortment events since 2023 and exhibited critical mutations in HA, M1, and NS genes, but lacked critical mutations in PB2 and PB1 genes that enhance virulence or adaptation to mammals. A human case with the PB2 E627K mutation was identified, highlighting the potential for rapid evolution post-infection. The virus was detected in dairy cattle, domestic cats, and wild birds in Texas, and confirmed by the National Veterinary Service Laboratories. Genomic analysis revealed that the virus is a reassortant of genotype B3.7 and a low pathogenic avian influenza virus. The virus showed high nucleotide identity in its genome sequences, forming a distinct phylogenetic subcluster. The detection of the virus in bovine milk raises public health concerns related to zoonotic transmission through unpasteurized milk. The virus was also detected in dairy herds in Idaho, Michigan, Ohio, North Carolina, and South Dakota, and in a human case after contact with infected dairy cattle. The virus's ability to spread through migratory birds and global trade networks has led to its dissemination across multiple continents. The virus's potential for adaptation to mammalian hosts and its ability to evolve rapidly pose significant public health risks. The study highlights the need for continued surveillance and monitoring to assess the virus's impact on human health and to develop strategies for prevention and control.