GEOFF BENNETT: California Governor Gavin Newsom declared a state of emergency yesterday in response to bird flu that's spreading among that state's dairy cows.

The virus has already caused the deaths of more than 120 million birds across the country since 2022.

Stephanie Sy reports now on the news from Colorado on efforts to keep the dairy work force safe, given concerns that, the more the virus spreads, the greater the possibility that it mutates to allow spread among humans.

STEPHANIE SY: In this stretch of rural Colorado, Soraya Leon is a lifeline for many agricultural workers.

SORAYA LEON, Community Health Worker, Project Protect: The farmworkers and dairy workers, it's very hard.

It's very hard to survive.

STEPHANIE SY: She's a community health worker with Project Protect, part of a statewide nonprofit.

Her regular visits and food deliveries to farmworkers in need now includes a bag full of face shields and masks, the equipment that protects them from bird flu.

Since the spring, avian influenza has been spreading in dairy cattle and has infected about 60 farmworkers nationwide.

Despite the risks, this worker said he's gotten little information from his employer.

MAN (through translator): The owner, we never see him.

They're not interested in us.

STEPHANIE SY: Speaking to us anonymously because he is undocumented, he told us earlier this year he was ill and had conjunctivitis.

Commonly known as pink eye, the symptom is a sign of possible infection from this strain of bird flu.

SORAYA LEON: On a statistic, we don't have too much people sick from this fever.

But on the reality, many people got sick, but they never know, because they never had information about what the symptoms are or how they feel.

STEPHANIE SY: Leon is part of a network of so-called promotoras established during COVID to help spread critical information to Colorado's many Hispanic farmworkers.

Lately, the promotora network has shifted to addressing the threat from bird flu.

Did workers get enough information when bird flu started circulating in this area over the summer?

SORAYA LEON: Not really.

The government response was too late.

They know they have the sickness because the symptoms, the eyes, and the cows.

So now they know they got this sickness, but only because we provide information later, not before.

STEPHANIE SY: In addition to groups like Project Protect, a federally funded agricultural health and safety center at Colorado State University has been using social media to provide information to workers.

While the virus, known as H5N1, has killed more than 100 million poultry birds and tens of thousands of Marine mammals, in cows, it has been less deadly, with most recovering after experiencing a drop in milk production.

While at least one person has been hospitalized with bird flu, this recent strain of the virus circulating in cows has been relatively mild in humans, and the risk to the public remains low.

But Colorado state veterinarian Maggie Baldwin and state epidemiologist Rachel Herlihy are watching the changes in the pathogen closely.

DR. MAGGIE BALDWIN, Colorado State Veterinarian: We have seen this virus move from species to species before.

We have seen spillover of this virus from wild birds and from poultry to mammals, and particularly that's been wild mammals in the past.

What's concerning is the mammal-to-mammal transmission of the virus right now.

STEPHANIE SY: While pasteurization has been shown to kill the virus in milk and dairy products, workers coming into contact with raw milk are at risk.

DR. RACHEL HERLIHY, Colorado State Epidemiologist: We know that the more opportunities that we give this virus to be exposed to people, the more opportunities it has to adapt potentially and then gain that ability to potentially spread from person to person.

And that's, of course, what we want to prevent.

STEPHANIE SY: Since July, Colorado has mandated weekly bird flu testing of bulk milk samples from its licensed dairies.

DR. MAGGIE BALDWIN: Every week, we have seen fewer and fewer positives, which is fantastic news.

But we really don't know what the long-term impact of this virus looks like.

We know that, yes, the dairy cows do seem to build some level of an immune response, but we don't know if an infected herd could become reinfected.

And dairy herds are constantly bringing in new replacement animals all the time.

STEPHANIE SY: Over the summer, more than half of the dairy herds in Colorado tested positive for avian influenza.

While there hasn't been a positive case since August, there's still concern about dairy farmworkers, many of whom are undocumented immigrants.

MAN (through translator): There really is very little support.

STEPHANIE SY: At a Mexican restaurant, we met one longtime dairy worker who also wanted to remain anonymous because of his immigration status.

Have companies given the right protections to farmworkers to keep them safe?

MAN (through translator): There really weren't any measures taken.

The only measure to avoid infection was when they washed the tires of the trailer trucks that arrived to drop off the feed.

But as far as the personnel, I never saw them wearing any protective gear to avoid infection.

STEPHANIE SY: He described a friend who got sick and said the lack of paid sick leave makes workers hesitant to report their illnesses.

MAN (through translator): From the moment a worker gets sick and stops working, he doesn't get anything.

STEPHANIE SY: Community health worker Soraya Leon says there are also issues with access to clinics and the cost of care.

Immigration status also plays a role in workers not getting tested.

SORAYA LEON: Undocumented people, they don't say anything because they are afraid all the time.

STEPHANIE SY: Zach Riley with the Colorado Livestock Association says the industry has been a crucial partner with state officials in protecting animal and worker health.

ZACH RILEY, Colorado Livestock Association: There's been multiple free resources provided by the state and by employers to try to make sure that you are protected.

I would say you would be hard-pressed to find somebody not doing it.

STEPHANIE SY: I mean, we did speak to some farmworkers who said, without the help of these nonprofit organizations, might not have had the information or the PPE at their disposal.

ZACH RILEY: I would venture to guess that's a very limited case and very limited number of those.

Any one of our producers would gladly tell you they're offering a whole treasure trove of things to their employees.

STEPHANIE SY: But despite efforts to reach out to several different cattle organizations, including Riley's, we couldn't find a Colorado dairy farmer to speak with us, some citing concerns around the potential spread of bird flu.

In November, research from Colorado and Michigan confirmed what many people suspected.

Antibody tests showed more farmworkers had signs of previous bird flu infections.

DR. RACHEL HERLIHY: That is not uncommon when it comes to infectious diseases, because not everyone gets tested.

But it does tell us that we still have work to do to protect humans from exposure.

STEPHANIE SY: Back at El Centenario Mexican restaurant, this dairy worker agreed that more support is needed.

MAN (through translator): Most people who work on dairy farms.

Most of us lack someone to tell us what guarantees we have.

We are really lacking information.

STEPHANIE SY: While there haven't been recent cases of bird flu in Colorado, dairy herds, the virus is continuing to spread widely in California cows.

Earlier this month, federal ag regulators took Colorado's lead and announced mandatory milk testing for the first time, an acknowledgement that we are still a long ways from getting a handle on the spread of this disease.

For the "PBS News Hour," I'm Stephanie Sy in Weld County, Colorado.