Some milk from Texas and Kansas dairy cows has tested positive for bird flu, US health officials announced on Monday – but they added that the country’s commercial milk supply is safe, and the risk to people remains low.

It marks the first known time avian influenza, otherwise known as bird flu, has been found in livestock. And in response, dairy industry officials said that producers have begun enhanced biosecurity efforts on US farms, including limiting the amount of traffic into and out of properties and restricting visits to employees and essential personnel.

However, while sporadic human infections with bird flu viruses have occurred, the US Centers for Disease Control and Prevention (CDC) said such viruses “do not normally infect humans”.

Officials with the Texas animal health commission confirmed the flu virus is the type A H5N1 strain, known for decades to cause outbreaks in birds and to occasionally infect people. The virus is affecting older dairy cows in those states and in New Mexico, causing symptoms such as a “drop in milk production, loss of appetite, and changes in manure consistency”.

It comes a week after officials in Minnesota announced that goats on a farm where there had been an outbreak of bird flu among poultry were diagnosed with the virus.

US dairies are required to only permit milk from healthy animals to enter the food supply chain.

Meanwhile, milk from the sick animals is being diverted or destroyed.

And in the rare event contaminated milk enters the food supply, pasteurization – a process is required for milk sold through interstate commerce – also kills viruses and other bacteria, the US Department of Agriculture (USDA) said.

“At this stage, there is no concern about the safety of the commercial milk supply or that this circumstance poses a risk to consumer health,” the agency said in a statement.

The federal government said its tests on the cattle did not detect any changes to the virus that would make it spread more easily to people.

While Texas agriculture officials believe cattle are expected to recover, the outbreak may have negative economic consequences for some dairy facilities.

“Herds that are greatly impacted may lose up to 40% of their milk production for seven to 10 days until symptoms subside,” the Texas department of agriculture said.

For the general public however, the USDA said any “milk loss resulting from symptomatic cattle to date is too limited to have a major impact on supply”. And the price of milk and other dairy products will not be affected, the USDA said.

Dairy farmers in Texas – a state that ranks fourth in milk production nationwide – initially became concerned three weeks ago when cattle started falling ill with what officials called “mystery dairy cow disease”, the Texas department of agriculture commissioner, Sid Miller, said. Milk production fell sharply and the cows were lethargic and were not eating much.

“We hadn’t seen anything like it before,” he said. “It was kind of like they had a cold.”

But Miller underscored that any contaminated milk had “all been dumped”.

The state’s animal health commission began an investigation that included tests for bird flu, spokesperson Erin Robinson said. Based on findings from Texas, USDA officials think the cows got the virus from infected wild birds.

Experts say livestock appear to recover on their own within seven to 10 days. That’s different than bird flu outbreaks in poultry, which necessitate killing flocks to get rid of the virus. Since 2022, outbreaks have led to the loss of about 80 million birds in US commercial flocks.

So far, the virus appears to be infecting about 10% of lactating dairy cows in the affected herds, said Michael Payne, a food animal veterinarian and biosecurity expert with the University of California, Davis’s Western Institute for Food Safety and Security.

“This doesn’t look anything like the high-path influenza in bird flocks,” he said.

Bird flu was detected in unpasteurized, clinical samples of milk from sick cattle collected from two dairy farms in Kansas and one in Texas. The virus was also found in a nose and throat swab from another dairy in Texas.

Officials called it a rapidly evolving situation. The Food and Drug Administration and CDC are involved, along with officials in the three states. Another dairy-heavy state, Iowa, said it was monitoring the situation.

Bird flu previously has been reported in 48 different mammal species, Payne noted, adding: “It was probably only a matter of time before avian influenza made its way to ruminants.”