Bird Flu Confirmed in U.S. Dairy Cows for the First Time, but Milk Supply Is Unaffected, Officials Say

Tests detected the virus at two farms in Texas and two farms in Kansas, but officials and scientists stress commercial dairy products remain safe to consume

A close-up of a dairy cow looking through a gap in a metal fence.
State and federal officials say the milk from the infected cows had been discarded and destroyed. This cow, photographed in 2016, is not one of those infected. Farm Watch via Flickr CC BY 2.0 DEED

Millions of domestic fowl and hundreds of thousands of migratory birds around the world have died over the past four years, as the spread of highly pathogenic avian influenza (HPAI), more commonly known as bird flu, continues to grip the globe.

As the disease spread, health officials confirmed the conveyance of the H5N1 strain from birds to mammals, including seals and sea lions on the coasts of Peru, Chile and Maine; bears in Alaska and Montana; and a single juvenile goat in Minnesota that, just last week, marked the first livestock in the U.S. to become infected.

And on Monday, federal and state health officials confirmed that dairy cows in Texas and Kansas have also contracted H5N1. Unpasteurized milk samples from at least three farms contained the virus, and a throat swab test of a cow came back positive. Cows in New Mexico have also been reported sick, with the affected animals—which are primarily older—exhibiting fever, eating less, lactating less and producing thick and discolored milk.

But officials and scientists stress that neither the states’ nor country’s milk supply is being affected.

“There is no threat to the public and there will be no supply shortages,” Sid Miller, commissioner of the Texas Department of Agriculture, says in a statement. “No contaminated milk is known to have entered the food chain; it has all been dumped. In the rare event that some affected milk enters the food chain, the pasteurization process will kill the virus.”

Black and white dairy cows lined shoulder to shoulder in the UK
Two farms in Texas and two farms in Kansas confirmed cases of bird flu in dairy cows. The animals in this picture are not from those farms. Iain Farrell via Flickr CC BY-ND 2.0 DEED

“[The virus] has only been found in milk that is grossly abnormal” and was discarded, Jim Lowe, a veterinarian and influenza researcher at the University of Illinois at Urbana-Champaign, tells the New York Times’ Emily Anthes.

Preliminary testing of affected Texas dairy cows has so far shown “consistency with the strain seen in wild birds,” a USDA official tells Science’s Jon Cohen. That indicates the strain has no known genetic mutations that would make it more transmissible. And researchers have not found evidence that the spread of H5N1 to cows indicates any greater likelihood of its transmission to humans, for whom both catching and spreading past strains of bird flu has been very rare.

Still, it is surprising that cows—which were assumed not to be susceptible to H5N1—came down with the virus. A current research priority is identifying the source of transmission, says Richard Webby, an animal influenza researcher at St. Jude Children’s Research Hospital, to New Scientist’s Grace Wade.

A light brown dairy cow stands amidst a crowd of black dairy cows
A dairy cow in Puerto Rico in 2018. Early research suggests the strain of H5N1 in the infected cows in the U.S. is the same one that has infected birds. USDA

The worst-case scenario, he adds, would be the discovery that H5N1 on these farms spread from cow to cow—which would be the first evidence that bird flu can be transmitted between mammals, indicating a much more serious problem.

But signs are pointing to this not being the case, with infected birds likely spreading the virus to livestock by contaminating their food or water sources. “You get onto a farm, especially during the migratory season, and you’ve got geese and ducks looking for feed just like everyone else,” Joe Armstrong, a veterinarian and cattle production expert at the University of Minnesota Extension, tells the New York Times. “To me that’s the most likely route.”

No cows have died yet from the virus, and unlike flocks of birds—which, when infected with HPAI, need to be culled to eliminate the virus—livestock are expected to recover on their own. So far, none of the cows have died from H5N1.

“Thankfully, research to date has shown mammals appear to be dead-end hosts, which means they’re unlikely to spread HPAI further,” Brian Hoefs, a veterinarian and the executive director of the Minnesota Board of Animal Health, said in a statement last week. He tells the Washington Post’s Andrew Jeong that the infected cows are likely to “fully recover.”

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