Global health alert issued as 'bird flu' transmission to humans confirmed, officials scramble for containment

A key latency in the blood testing of exposed workers might result in an underestimating of the virus's potential transmission to people, experts and researchers cautioned almost immediately after the H5N1 avian flu outbreak across American farms and ranches earlier this year.

Human-to-human 'bird flu' transmission reported, health officials intensify efforts to prevent pandemic.

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Those warnings have proven prescient. And the government Centers for Disease Prevention and Control (CDC) is now not only attempting to slow the spread of the virus, but also catching up on testing procedures that have been widely opposed by American farmers.

The question today is if novel measures can prevent widespread human-to-human transmission of this strain—as some scientists believe it is only a matter of time.

"We will have a bird flu pandemic," former CDC director Robert Redfield said plainly in a June television appearance. "The question isn't if, but when... The pandemic will occur when the virus is able to bind to a human receptor and then spread from person to person.

A CDC research released on Thursday did nothing to soothe such concerns. The investigation discovered that a high number of H5N1 infections went unreported in dairy workers who worked on farms with cows that tested positive for the virus last summer. Eight of the 115 farm workers who underwent blood testing in Michigan and Colorado showed signs of recent infection in the form of antibodies, although only half of them remembered experiencing symptoms. "All eight had either milked cows or cleaned the milking mechanisms," authorities added.

Among other things, the findings suggest that many more American farm workers may have become infected with the virus without realizing it—all the more reason, experts say, for federal and state health agencies to aggressively offer testing and enhanced personal protective equipment (PPE) to those who work on dairy and poultry farms in the United States.

"This largely verifies what we suspected: More individuals are becoming sick on farms than the official count. Amesh Adalja, senior scholar at the Johns Hopkins University Center for Health Security, believes the serology backs this up. "That's the reason why so many of us have been wanting more aggressive serological testing on farms, in order to understand the extent of infection and better understand the risks that the virus poses (there)."

During a news event on Thursday, CDC primary deputy director Nirav Shah stated that nothing in the new data "gives rise to a concern about person-to-person transmission," and that the agency believes the virus still offers a minimal risk to the public.

In the United Kingdom, however, government officials have already upped the bird flu virus risk rating from medium to high. In the United States, human H5N1 incidences are increasing in California and Washington. During the 2024 outbreak, 46 human cases have been identified and verified nationwide, including one in Missouri who had no known connection to cattle or poultry, the two leading sources of exposure thus far. All of the people have had relatively minor symptoms, such as conjunctivitis or coughing, and none have been hospitalized.

Since the beginning of this year's H5N1 outbreak, federal and state agencies have struggled to perform appropriate testing on farms and among farm workers. The reasons are numerous, but include the fact that farmers fear that if positive cases are identified, their operations will be curtailed, and that many immigrant workers do not want to interact with any government officials, let alone submit to blood testing or risk being forced to stay home from work and not being paid if they test positive.

The CDC lacks the authority to force testing, but the discovery of asymptomatic cases or cases so mild as to be undetectable may prompt more forceful recommendations from it and local health agencies, even if those who have long studied bird flu and other similar viruses aren't surprised to learn that some people were unaware they had been infected.

"I don't think anything is particularly surprising," says Richard Webby, an infectious disease researcher at St. Jude Children's Research Hospital in Memphis and head of the World Health Organization Collaborating Centre for Studies on the Ecology of Influenza in Animals and Birds.

According to Webby, asymptomatic infection instances are "absolutely anticipated" with nearly all infectious diseases, but particularly with respiratory ones. The potential for H5N1 to spread covertly from those who are unaware they are afflicted, however, may provide its own issue. While there has been no evidence of human-to-human transmission, researchers are concerned that if this occurs, it would be disastrous.

"I don't think it's a foregone conclusion that H5N1 is going to be the cause of the next pandemic, but certainly an avian influenza virus in the future will be," Adalja adds. "And I think we need to get this one right. Even if it doesn't trigger a pandemic, we want to think of this as a trial run—and we're not performing a very good trial run with this virus."

The CDC advised Thursday that agricultural workers who have had considerable bird flu exposure be tested for H5N1, whether or not they have symptoms, a precaution that might be critical once the typical flu season begins and distinguishing between viruses becomes more difficult. "The best way to limit the virus's room to run is to test, identify, treat and isolate as many cases as possible in humans and as quickly as possible," Shah told reporters.

The agency also wants the antiviral Tamiflu made available to workers who had a high-risk exposure to H5N1-infected animals, particularly those who did not wear proper PPE. Finally, the FDA revised its recommendations to prioritize additional PPE for people involved in higher-risk jobs, such as milking parlors or poultry culling operations.

The California Department of Public Health, along with some other states, has previously supplied personal protective equipment to dairy farms and their workers. But, like other health organizations, it cannot compel employees to wear them. Anecdotally, this has been an issue throughout the country, since workers frequently avoid the gear in hot, suffocating conditions.

In a separate paper released Thursday, dairy farm workers in Colorado verified that the hot, humid conditions common in milking parlors can make wearing respirators and masks uncomfortable. Especially during the summer, this might result in fewer covered workers. Even among those who use masks, PPE deterioration is typical when workers come into contact with tainted milk or animal waste.

It creates a risky situation in which unprotected personnel operate in close proximity to diseased dairy cows, where infection can be as easy as being splashed with contaminated milk during the milking process. According to researchers, this is precisely why health organizations must increase their efforts to provide PPE education and services.

"It can be probably hard to use a lot of this PPE," Webby said. "But I believe conveying it (is vital) so that those who are at risk understand that there is a risk and that their PPE may assist protect them. Even if it isn't something they can wear all the time, anything is preferable to nothing. And message is the key."

Such message was almost non-existent in the early months of H5N1's march through America's dairy and poultry farms earlier this year. According to Vanity Fair, Agriculture Secretary Thomas Vilsack informed scientific professionals about the avian flu in June that "it's just going to burn itself out."

Now, those health authorities and the organizations they lead are trying to discover methods to protect both humans and cattle from a virus that has already affected 446 dairy cows in 15 states and more than 100 million birds, largely commercial poultry, in addition to the reported human cases. Bird flu's reported 52% fatality rate in Europe since 2002 serves as a stark reminder of the stakes—only dramatically increased preventive, testing, and treatment efforts, as well as total public disclosure about the results of those efforts, will suffice.

Adalja and other specialists believe that the H5N1 subtype seen in dairy cows in the United States is not as harmful in humans as other clades. Still, "what is concerning is the fact that this has been something that's been allowed to get this way," Adalja tells me. "This is something that many of us in the field have been talking about being more aggressive about for months."

The clock is ticking louder.