Highly Pathogenic Avian Influenza in Dairy Cattle - 2025 Update

As many of you would be aware there has been an ongoing outbreak of H5N1 Avian Influenza, also known as HPAI (Highly Pathogenic Avian Influenza) in dairy herds across the US.  The current US outbreak started in wild and domestic birds in January 2022 and has resulted in millions of bird deaths across all 50 states.

The virus was first detected in a dairy herd in March 2024 in Texas and has since spread to 1053 herds in 17 states across the US. The response by the US government has varied depending on the state and include stock movement bans, import bans, weekly testing of bulk milk, bans on the sale of unpasturised milk and government enforced farm biosecurity protocols.

Clinical signs of HPAI in dairy cattle include high fever, loss of appetite, milk drop, respiratory disease and mastitis presenting as thick colostrum-like milk (usually in all 4 quarters).  Death and culling rates have been low (2%) with most infected cows recovering uneventfully with supportive treatment. Direct transmission of the virus between dairy cows has been demonstrated and it has detected in birds, cats, and foxes on infected farms.  The virus can infect people with 70 confirmed cases so far with most people having conjunctivitis as the main clinical sign, but some have developed more severe flu-like symptoms.  There has been one death caused by HPAI.

The current position of our government is that the presence of H5N1 HPAI in dairy cattle in the US does not increase the risk of an incursion into Australia, however the risk of H5N1 entering Australia through migratory birds remains moderate. The risk of the current strains of AI present in Australia jumping species from birds to cattle is considered to be low. However, vigilance is always prudent - if you have a sudden outbreak of deaths / severe respiratory signs in any poultry or wild birds or an outbreak of disease in cattle that is consistent with HPAI, contact your private vet or government vet ASAP.