USDA Confirms Avian Flu in Two Washington Dairy Herds
The Animal and Plant Health Inspection Service, part of the US Department of Agriculture, identified HPAI H5 clade 2.3.4.4b in the two herds. Before the findings, Washington’s commercial dairy sector had repeatedly tested negative through state and federal surveillance programmes.
Laboratories at the National Veterinary Services Laboratories in Ames, Iowa, are conducting whole-genome sequencing. The work is intended to establish whether the virus belongs to the bovine B3.13 lineage, the D1.1 genotype or a separate spillover from wild waterfowl.
Confirmed infections require farms to isolate affected animals and divert milk under federal and state procedures. Milk from cows showing clinical signs cannot enter commercial food channels and must be destroyed on the farm. Haulers and processors are also required to clean tankers, hoses and receiving areas to reduce the risk of mechanical transmission between premises.
Fluid-milk bottlers, cheese plants and drying facilities in the Pacific Northwest have strengthened quality-control measures. Federal food-safety testing has found that commercial pasteurisation inactivates influenza viruses, and processed dairy products remain safe for consumers under those procedures.
The detections extend national disease monitoring into a Pacific Northwest dairy region that had remained free of the virus for months. Washington’s cases have also drawn attention to the Pacific Flyway, where autumn bird migration can increase contact risks around open feed areas, uncovered dry lots and wastewater lagoons. International buyers monitor US disease surveillance, and federal authorities are reporting the cases while containment work proceeds.
At affected farms, clinical illness can reduce daily milk output by 10-20% during its peak. Cows generally recover within several weeks, unlike poultry flocks, which may be subject to complete depopulation. Producers also face costs for veterinary support, anti-inflammatory treatment, extra labour for isolation and additional sanitation. USDA assistance, including the Emergency Assistance for Livestock, Honeybees, and Farm-raised Fish programme and compensation mechanisms for lost production, is available to help cover losses and biosecurity measures.
The Washington State Department of Agriculture and APHIS epidemiologists are tracing vehicle movements, shared equipment and personnel transfers linked to neighbouring facilities. Dairy groups and veterinary extension teams have advised producers to limit non-essential visitors, disinfect livestock trailers before and after journeys and keep cattle away from open surface water. The sequencing results are expected to add epidemiological information for ongoing field trials of bovine H5N1 vaccines.
