USDA confirmation of highly pathogenic avian influenza in two Washington dairy herds has added a new state to the livestock dimension of the HPAI response, sharpening the economic case for surveillance and farm biosecurity even as the commercial milk supply remains safe. The 8 October finding is Washington's first confirmed HPAI detection in livestock, according to the US Department of Agriculture's Animal and Plant Health Inspection Service.

APHIS said its National Veterinary Services Laboratories confirmed H5 clade 2.3.4.4b by PCR in two dairy herds after animals showed clinical signs consistent with avian influenza. The agency said the herds had previously tested negative through routine surveillance under the National Milk Testing Strategy. Genetic sequencing is to be completed, while APHIS and the Washington Department of Agriculture carry out on-farm investigations, diagnostic testing and epidemiological work.

The event does not change USDA's eradication strategy, APHIS said. But it shows why an apparently negative surveillance history cannot be treated as permanent protection. For dairy operators, the operational burden of enhanced biosecurity, reporting and testing is weighed against the potentially higher cost of disease spread, disruption to milk handling and loss of market confidence. APHIS said financial assistance is available to strengthen biosecurity and offset HPAI-related costs.

Food-supply messaging is equally important to the sector. USDA stated that the detection does not affect the safety of the commercial milk supply and that pasteurisation is effective at inactivating the virus. Dairies may send only milk from healthy animals for human consumption; milk from affected animals is diverted from the commercial tank or destroyed. Those controls help separate farm-level disease management from consumer-facing food-safety risk.

Dairy cattle in 19 US states have been infected since the outbreak began in March 2024, although APHIS said cases had occurred in only a small number of states this year before the Washington confirmation. The immediate commercial test is not just containment at the two holdings. It is whether diagnostic capacity, producer participation and biosecurity support can keep a local detection from becoming a wider production and logistics problem.

For more information: USDA APHIS