April 16, 2025

Number of US dairy cattle found with H5N1 at 1,000

The US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) on April 9 reported two more H5N1 avian flu detections in US dairy herds, one in California and the other in Nevada, raising the United States' total to 1,000 since March 2024.

California has been the hardest-hit US state, and though detections have dropped sharply, sporadic H5N1 confirmations continue and have now reached 759 in the state. In December 2024 when the situation was intensifying in California dairy cattle with spread beyond the Central Valley, the state's governor announced a state of emergency to shore up California's response.

Nevada has now reported 11 outbreaks since December 2024. In early February, the USDA reported a new spillover from birds to cattle in the Nevada outbreak. It involves the D1.1 genotype, which is distinct from the B3.13 genotype implicated in earlier dairy cattle outbreaks.

Over the past two days, APHIS also confirmed two more detections in poultry flocks. They involve backyard birds in Colorado's Larimer County and another live-bird market in New York's Queens County.

Outbreaks of H5N1 in US poultry began in early 2022 and have led to the loss of more than 168 million birds across all 50 states and Puerto Rico.

- CIDRAP