The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) has confirmed two additional cases of highly pathogenic avian influenza (H5N1) in dairy herds—one in California and another in Nevada—bringing the nationwide total to 1,000 detections since March 2024.
California remains the most affected state, accounting for 759 of the total cases. Although the frequency of new detections has declined significantly in recent months, isolated confirmations continue to emerge. During the peak of the outbreak in late 2024, cases spread beyond California’s Central Valley, prompting a state of emergency to enhance containment and response efforts.
Nevada has now recorded 11 H5N1 outbreaks in dairy herds since December 2024. In February, officials identified a new bird-to-cattle transmission linked to the D1.1 virus genotype. This strain differs from the B3.13 genotype associated with earlier outbreaks in dairy cattle, suggesting continued viral evolution and multiple introduction events.
Authorities continue to monitor the situation and conduct genomic surveillance to understand the transmission dynamics and potential risks to livestock and public health.
