Investigations are under way into suspected outbreaks of highly pathogenic bird flu in dairy herds in the US, after tests have shown the pathogen to have been present in milk supplies across multiple states.

A “large representative national sample” of milk supplies are being assessed for presence of the disease.

The US Department of Agriculture (USDA), the Food and Drug Administration (FDA) and the Centres for Disease Control and Prevention (CDC) are among the agencies investigating the finding.

Both the FDA and the USDA have moved to state to consumers that commercial milk supplies remain safe due to pasteurisation and the diversion or destruction of milk from sick cows under the US’s federal-state milk safety systems.

Tests

“Based on available information, pasteurisation is likely to inactivate the virus, however the process is not expected to remove the presence of viral particles,” the USDA noted in saying that tests likely showed up virus particles which were no longer active.

The FDA has issued advice to US dairy farmers on the precautions they should take when disposing of milk from affected cows, so these supplies do not become a source of further infection.

These treatments include heat treating or pasteurising affected supplies before dumping into slurry stores which are biosecure and cannot be accessed by livestock or wildlife.

It also moved to reiterate its long-standing consumer recommendation that consumers should not drink raw milk or raw milk products.

The World Health Organisation (WHO) has labelled the transmission of the H5N1 strain of highly pathogenic bird flu to mammals, including humans, as a “significant public health concern”.

“The great concern, of course, is that in doing so and infecting ducks and chickens – but now increasingly mammals – that that virus now evolves and develops the ability to infect humans. And then critically, the ability to go from human-to-human transmission,” the WHO’s chief scientist Jeremy Farrar stated.

There have been no human-to-human cases of H5N1 transmission yet recorded.