H5N1 continues to circulate in U.S. dairy cattle, with a new cluster of detections in Washington adding to the outbreak’s geographic reach. Last week, the Washington State Department of Agriculture confirmed 34 affected dairy herds in the state: 33 in Yakima County and one in neighboring Benton County. The first two detections were confirmed Oct. 8, marking Washington’s first known cases in dairy cattle.
The Washington detections bring renewed attention to an outbreak that has affected dairy herds in 19 states since March 2024, according to the USDA. The virus identified in the initial Washington herds was the B3.13 strain, which has circulated in U.S. dairy cattle since spring 2024.
The outbreak has also had human health consequences: on Nov. 1, the Yakima Health District reported that a county resident hospitalized with severe avian influenza after exposure at a dairy with infected cattle had died. The district also reported a third confirmed human case in the county…