CDC reveals new data on bird flu in Michigan farmworkers as US case count ticks up

Whether it spread from sick cows or sick poultry to people, the type of H5N1 avian flu virus that infected a commercial poultry worker in Colorado earlier this month is very similar to the virus that sickened a Michigan dairy farmworker in May, according to new genetic sequencing test results released by the U.S. Centers for Disease Control and Prevention.

And that's good news, said CDC Director Dr. Mandy Cohen, who visited Michigan this week to talk with local and state health leaders about efforts to better understand how the virus is spreading to humans, whether it is mutating to become more dangerous or causing asymptomatic infections.

"We are taking the cases of avian flu that we are seeing very seriously, but I want folks to know the overall risk right now to the population is low," Cohen told the Free Press during a Tuesday morning visit to an immunization clinic at the DMC Children's Hospital of Michigan Specialty Center in Detroit. "That's because we've never seen a human-to-human transmission of that virus. But we also learned very much through COVID that these viruses like to change. So our work is now to make sure we're giving that virus less opportunity to change and potentially then become something that can transmit humans to human."

"We are doing two things: One, we want less virus to be circulating so that it has less chance to change. The other is get ready, be prepared. We want to make sure we have tests that are available, treatments that are available and vaccines that are available."

Since April, 11 poultry and dairy cattle workers in Texas, Michigan and Colorado have been sickened following exposure to infected animals.

Genetic sequencing tests suggest the subtype of the virus in a Colorado poultry worker is B3.13 clade 2.3.4.4b and hasn't mutated enough to easily spread from person to person, evade antiviral treatments, or cause more severe disease.

"The findings are reassuring, showing it is closely related to the first human case discovered in Michigan and that it does not have changes associated with antiviral resistance," the CDC wrote in an online update . "The full sequence was uploaded to a public database so that researchers in the U.S. and around the world can analyze it."

Has the risk to people from H5N1 bird flu risen?

Not yet.

"There are no changes to the virus that would suggest the risk to human health has increased," the CDC reported. "Overall, the genetic analysis of the HPAI A(H5N1) virus in Colorado supports CDC's conclusion that the human health risk currently remains low."

So far, all 11 people with known cases of H5N1 influenza A in the U.S. this year have had mild symptoms such as conjunctivitis, also known as pink eye, and/or upper respiratory symptoms.

But that hasn't always been the case with this elusive virus; other H5N1 subtypes that have spread globally since the late 1990s have had mortality rates that topped 50% , the CDC reported.

More: How Michigan became ground zero for H5 avian influenza in the US

More: Michigan’s top agricultural leader cautiously optimistic about bird flu in state

What else is known about the virus in Michigan?

To get a better idea of whether there is asymptomatic spread of the bird flu virus among Michigan dairy farmworkers, the state Department of Health and Human Services led a seroprevalence study in June that tested blood samples of 35 people who worked directly with cows sickened by H5N1 infections.

Many of the workers did not wear the recommended personal protective equipment such as N95 respirator masks or goggles around the animals, and had different jobs on farms across multiple Michigan counties. Most worked directly with the sick cows, the health department said.

The Michigan Department of Health and Human Services analyzed the blood samples, looking for antibodies, which are produced when people develop an immune response to a virus, suggesting they have been infected even if they didn't feel sick or had had only mild symptoms.

The CDC published preliminary results of that study July 19, finding:

• None of the 35 workers whose blood samples were analyzed developed neutralizing antibodies to the H5N1 avian influenza A virus, which suggests none of them had previous infections with the virus currently circulating in the U.S.
• Many of the farmworkers' blood samples showed neutralizing antibodies to seasonal flu viruses, which suggests they previously were vaccinated or infected with seasonal flu. It also means their bodies most likely could muster an immune response to seasonal flu viruses.

The seroprevalence tests are important, the CDC said, "because it suggests that asymptomatic infections in people are not occurring and provides support to the current testing approach — i.e., collecting samples from symptomatic people who have been exposed to sick animals."

What is the CDC doing to make sure it's ready if the H5N1 virus changes?

Cohen said the nation is in "a very different place" than it was at the start of the coronavirus pandemic, when scientists had to scramble to develop tests, vaccines and treatments.

"We have tests for avian flu that are specific," Cohen said. "We have them in all of our public health labs, and by the end of the year, we're working to have them in our commercial labs as well. We already have a treatment that is available — Tamiflu or oseltamivir. We have it not only in our pharmacies, but in our stockpiles as well.

"And then on vaccines, we have vaccine candidates. We learned from COVID that you want to match that vaccine with the exact ... type of virus that we see circulating. So we have candidates and we have the ability to scale up rapidly. So that's what we're focused on.

"We do have vaccine that is matched to the current strain, but we're seeing mild disease right now. ... What we are thinking about is if the virus were to change and get the ability to spread human to human, that would be when we'd scale up production. That is waiting in the wings."

What is the scope of the H5N1 virus spread in Michigan and the U.S.?

The H5N1 bird flu virus has been spreading for two years among wild birds and domestic poultry — forcing poultry farmers and egg producers in Michigan and across the country to cull millions of birds.

The virus adapted to infect mammals and leapt to cows in late 2023, with high levels of viral particles identified in the milk and udders of sick livestock. Since then, the virus has been identified in cattle on 26 dairy farms in 10 Michigan counties : Allegan, Barry, Calhoun, Clinton, Gratiot, Ingham, Ionia, Isabella, Montcalm and Ottawa counties, according to the state Department of Agriculture and Rural Development. The disease also has been detected in dairy herds in 12 other states, according to the U.S. Department of Agriculture.

Four U.S. dairy farmworkers have contracted bird flu after working closely with infected cows; two worked on Michigan farms, the CDC reported. The other confirmed U.S. human cases of bird flu this year have occurred among workers at two separate commercial egg-laying operations in Colorado, where the employees were culling infected chickens.

Who is at highest risk for bird flu infection?

Workers on dairy cattle and poultry farms, at commercial egg-laying operations, slaughterhouses and meat-processing plants, as well as people who have close or prolonged, unprotected exposures to infected animals or their environments are at greater risk of H5N1 infection.

The CDC recommends:

• Avoiding unprotected exposure to sick or dead animals, including wild birds, poultry, dairy cattle and other animals, as well as with their feces or other materials that could be infected with H5N1 viral particles.
• Wearing personal protective equipment (PPE) if direct or close contact with sick or dead animals, feces, or other materials potentially contaminated with H5N1 viral particles can't be avoided. That PPE should include safety goggles, disposable gloves, boots or boot covers, a particulate respirator such as an N95 filtering facepiece respirator that has been fit-tested, disposable fluid-resistant coveralls, and disposable head cover or hair cover.
• Anyone exposed to H5N1-infected birds or other animals should monitor themselves for new respiratory illness symptoms, including pink eye, beginning after their first exposure and for 10 days after their last exposure.
• If anyone who had close contact with infected animals develops symptoms, state and federal health leaders recommend seeking medical care for evaluation, testing and treatment. If you are symptomatic, you should isolate from others until infection is ruled out (except to seek medical care).

Are eggs, beef, dairy products and chicken safe to eat?

Yes, so long as you fully cook your eggs, chicken and beef and consume only pasteurized dairy products, the U.S. Food and Drug Administration says.

Although the FDA detected fragments of the H5N1 virus in the commercial pasteurized milk supply, the particles are not capable of replicating or causing disease.

Contact Kristen Shamus: kshamus@freepress.com. Subscribe to the Free Press.

This article originally appeared on Detroit Free Press: CDC reveals new data on bird flu in Michigan farmworkers as US case count ticks up