Bird flu hits dairy herds across the United States

Authorities are warning producers to isolate affected animals after concerns transmission is occurring between cows.

The United States Department of Agriculture confirmed on March 25 the highly pathogenic avian influenza (HPAI) had been detected in two dairy herds in Texas and two dairy herds in Kansas.

The USDA's National Veterinary Services Laboratories (NVSL) later confirmed the presence of HPAI in a Michigan dairy herd that had recently received cows from Texas.

Dairy herds in New Mexico and Idaho were also positive to initial testing - but are still awaiting final confirmation of the disease from the NVSL.

Wild migratory birds are believed to be the source of infection - likely pigeons, blackbirds and grackles in Texas.

At this stage the disease is causing lower milk production, lower appetite and other symptoms in affected animals, but most have recovered after isolation with little to no associated mortality reported.

The USDA said the spread of symptoms among the Michigan herd meant it could not rule out transmission between cattle.

"USDA and partners continue to monitor this closely and have advised veterinarians and producers to practice good biosecurity, test animals before necessary movements, minimise animal movements and isolate sick cattle from the herd," it said.

At this stage, there appears to be no threat to people from the outbreak

Initial testing has not found changes to the virus that would make it more transmissible to humans.

"While cases among humans in direct contact with infected animals are possible, this indicates that the current risk to the public remains low," the USDA said.

There was no concern about the safety of the commercial milk supply because products were pasteurised before entering the market.

But the US Food and Drug Authority has warned consumer about the risks associated with raw milk consumption.

"FDA's longstanding position is that unpasteurised, raw milk can harbour dangerous microorganisms that can pose serious health risks to consumers," the FDA said.

It is recommending no manufacture or sale of raw milk or raw/unpasteurised milk cheese products made with milk from cows showing symptoms of illness.

It is also recommending if the milk from cows showing symptoms is to be used for calf feeding, it should be heat treated first.

According to the Australian Department of Agriculture, Fisheries and Forestry, Australia is currently free of HPAI.

It said avian influenza was a viral disease of birds and was found across the globe.

Avian influenza virus strains were described as low pathogenicity (LPAI) or high pathogenicity (HPAI).

Most LPAI strains of avian influenza virus caused minimal disease in wild birds and poultry.

However, some LPAI strains could evolve into HPAI strains when they spread among poultry.

DAFF said the strain of HPAI detected in the US dairy herds was spreading globally, causing widescale outbreaks.

"These have caused extensive losses of poultry and wild birds, and spillover infections in mammals," DAFF said.

"This strain has not been detected in Australia, but there are concerns about the potential impacts on poultry and wildlife if it arrives on our shores."