The California Department of Public Health’s One Health Response to H5N1
August 4, 2025
On July 14, 2022, highly pathogenic avian influenza A(H5N1) clade 2.3.4.4.b was detected for the first time in California wild birds. By the end of August 2024, nearly 600 confirmed positive wild birds and over 7.1 million domestic birds had been impacted by H5N1 in California, and H5N1 infection was detected in three dairy herds in the Central Valley.
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