Sick dairy cattle in two central U.S. states have tested positive for bird flu, federal officials said Monday.

As of Monday the highly-contagious pathogenic avian influenza virus (HPAI) had been found in unpasteurized, clinical samples of milk from ill cows at two dairy farms in Kansas and one in Texas, and a swab from another dairy cow in Texas, The U.S. Department of Agriculture announced in a press release.

The agency said its officials, along with the Food and Drug Administration, Centers for Disease Control and Prevention (CDC), and state veterinary and public health officials, are investigating an illness detected primarily in older dairy cows in those states, as well as in New Mexico.

Wild migratory birds are believed to be the source of the infection, the USDA wrote, and viral testing and epidemiologic efforts are continuing this week.

Are manatees endangered?Here's the current conservation status of the marine mammal.

Farms in Texas, Kansas report finding dead birds on properties

Additional testing took place Friday and over the weekend, the USDA reported, because farms have also reported finding dead wild birds on their properties.

Based on findings from Texas, the agency wrote in the release, the detections appear to have been introduced by wild birds and commercial milk supply "remains safe due to both federal animal health requirements and pasteurization."

Bird flu spread to humans is low risk, USDA says

Initial testing by the National Veterinary Services Laboratories has not found changes to the virus that would make it more transmissible to humans which, the USDA said, means the risk to the public contracting the virus remains low for now.

Federal and state agencies said they "are moving quickly" to conduct additional bird flu testing.

"The first detection of HPAI in dairy cattle in Texas and Kansas underscores the importance of adherence to biosecurity measures, vigilance in monitoring for disease, and immediately involving your veterinarian when something seems ‘off’," AMVA President Dr. Rena Carlson said. "A complete evaluation, including the collection and submission of laboratory samples and reporting to state animal health officials when appropriate, and in a timely fashion, are incredibly important."

Bird flu in Texas, Kansas affecting older dairy cows

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, the state agency said, is affecting older dairy cows in Texas and Kansas, as well as cattle in in New Mexico, causing symptoms including decreased lactation and low appetite.

Breaking:Baltimore's Key Bridge collapses after ship collision; 2 rescued, search continues: Live updates

What is the bird flu? 

The bird flu is a disease caused by a family of flu viruses primarily transmitted between birds.

Avian influenza viruses, according to the CDC and USDA, are classified into two groups: Low Pathogenic Avian Influenza (LPAI) (often seen in wild birds) and HPAI, found mostly in domestic poultry. According to the Centers for Disease Control, LPAI viruses cause mild or no disease and HPAI cause severe disease and high mortality rates in infected birds.

The bird flu has cost the government roughly $660 million and in recent times raised the price of eggs and poultry. At least 58 million birds were slaughtered last year to limit the spread of the virus.

What are signs of bird flu?

Symptoms of bird flu include:

• Loss of appetite, lethargy
• Sudden death without prior symptoms
• Eyelid swelling
• Twisting of the head and neck
• Purple discoloration to body parts including legs

'No concern' about commercial milk supply safety

"At this stage," the USDA wrote, there is "no concern about the safety of the commercial milk supply or that this circumstance poses a risk to consumer health."

Dairies are required to send milk from healthy animals into processing before it can be put on grocery shelves, the agency said, and the milk from the sick animals was being destroyed.

In addition, USDA officials said, pasteurization "has continually proven to inactivate bacteria and viruses," including influenza, in milk.

It's also mandated for milk entering interstate commerce.

"For the dairies whose herds are exhibiting symptoms, on average about ten percent of each affected herd appears to be impacted, with little to no associated mortality reported among the animals," the USDA wrote in its release. "Milk loss resulting from symptomatic cattle to date is too limited to have a major impact on supply and there should be no impact on the price of milk or other dairy products."

Natalie Neysa Alund is a senior reporter for USA TODAY. Reach her at [email protected] and follow her on X @nataliealund.