Updated April 1, 2024 at 4:21 PM ET
Livestock at multiple dairy farms across the U.S. have tested positive for bird flu — also known as highly pathogenic avian influenza, or HPAI — in an outbreak that's likely spread to at least five states.
The U.S. Department of Agriculture's Animal and Plant Health Inspection Service confirmed Friday that cows in Texas, Kansas and Michigan had been sickened by the virus, and there were presumptive positive test results for additional herds in New Mexico and Idaho.
It's the first time the disease has been found in dairy cattle, according to the American Veterinary Medical Association.
On Monday, the Texas Department of State Health Services announced that a person who was exposed to dairy cattle presumed to be infected with bird flu had also caught the virus.
It is only the second time a human in the U.S. has contracted HPAI A, or H5N1, according to the Centers for Disease Control and Prevention. A person in contact with infected poultry was sickened in Colorado in 2022.
Texas issued a public health alert Monday, asking health care providers in the state to be on the lookout for people with symptoms of bird flu who may have been exposed to an infected person or animal.
The new cases come just days after a group of young goats contracted bird flu on a Minnesota farm.
Bird flu infects the respiratory and gastrointestinal tracts of birds and is often fatal to avian populations. It can spread from wild birds to commercial poultry and backyard flocks as well as terrestrial and marine mammals and humans.
Government officials say the risk to the public amid the current outbreak remains low. Most past human infections have occurred after people had "unprotected exposures to sick or dead infected poultry," according to the CDC, and it's rare for a human to transmit the disease to another person.
Officials say the strain of the virus detected in Michigan is similar to the one found in Texas and Kansas, which was shown through initial testing not to include any changes that would make it more transmissible to humans.
The rash of bird flu infections should also not dramatically impact consumers of dairy products, federal and state officials say.
"The good news is this is not a serious problem," Texas Agriculture Commissioner Sid Miller told NPR on Sunday. "It's not going to bankrupt anybody. Cows basically have the flu for a week, and they get over it."
Officials say the dairy supply is safe
The country's commercial dairy supply is safe and a milk recall is unnecessary, the USDA says.
That's because dairies are required to divert or destroy any milk from impacted livestock, and only milk from healthy cows can be processed for human consumption.
Additionally, pasteurization — which is required for milk entering interstate commerce — kills bacteria and viruses, including influenza.
The Food and Drug Administration says there is limited information available about the transmission of bird flu in raw, unpasteurized milk. The agency has long warned people to avoid raw milk, which it says can harbor dangerous bacteria and sicken consumers.
Federal officials say the loss of milk from ill dairy cows is too limited to significantly impact the commercial supply, which is typically higher in the spring due to increased seasonal production. Dairy prices are not expected to rise due to the outbreak, they added.
How regulators and farmers are working to contain the spread
The USDA believes the dairy cows have been sickened by a strain called H5N1, Eurasian lineage goose/Guangdong clade 2.3.4.4b, which was likely introduced by wild birds. Pigeons, blackbirds and grackles were identified at the affected Texas farms.
But federal officials are also not ruling out the possibility of cow-to-cow transmission. That's after a Michigan farm recently received a shipment of cattle from an affected Texas farm before any of the cows show signs of disease, the Michigan Department of Agriculture and Rural Development said Friday.
While there are still many unknowns, the available evidence collected from infected cattle isn't alarming to Richard Webby, a virologist from Saint Jude Children's Research Hospital in Memphis, Tennessee.
"There's nothing in the sequence of the virus that sort of immediately screams that it has changed, and that's why these cows are getting infected," he said. "It just seems to be fairly typical of the viruses that have been detected in birds in various regions."
Cows sickened by bird flu at affected dairy farms have recovered "after isolation with little to no associated mortality reported," according to the USDA.
Texas officials said Monday that the person who tested positive for bird flu had reported eye inflammation, or conjunctivitis, as their only symptom. They were told to isolate and were being treated with oseltamivir, an antiviral drug.
Federal and state agencies are continuing to test sick livestock and unpasteurized milk samples.
The USDA also recommends that farmers and their veterinarians practice "good biosecurity," which includes limiting animal movements, testing livestock before they're moved and isolating sick cows.
NPR's Will Stone contributed reporting.
Copyright 2024 NPR. To see more, visit https://www.npr.org.