For nearly four months, the spread of bird flu in the nation’s dairy cattle has stoked fears that, if left unchecked, the virus could eventually unleash a pandemic.
The recent cluster of human cases connected to poultry farms in Colorado only underscores that the threat remains real.
Genetic sequencing of the virus collected from the sickened poultry workers closely resembles what’s circulating in dairy herds, suggesting that cattle somehow introduced the virus into the poultry flock.
At one massive poultry facility, workers culled the birds under particularly dangerous circumstances.
The outdoor temperature flirted with 100 degrees and heat advisories blanketed the region earlier this month as workers arrived at a commercial poultry operation in Weld County to start killing chickens.
Of the 1.8 million egg-laying hens inside the operation’s barns, at least some were infected with highly pathogenic avian influenza — bird flu. The strain of the virus that is now circling the globe has shown a remarkable ability to infect all kinds of animals, from seals to skunks to mountain lions. But it spreads most rapidly and lethally in wild birds and domestic poultry.
When a commercial flock is infected, standard practice is grim but efficient: Kill all the birds at the farm, devastating one operation in the hopes of stopping the virus and sparing the rest of the industry. By the time the workers in Weld County were done, though, some discovered that the virus had survived at least for one infection longer. It had found a new host: Their own bodies.
JUST HOW deadly is the H5N1 avian flu? The virus, which is currently sweeping through U.S. dairy herds, rarely jumps to human beings, at least for now. But when it does the consequences can be grave: The World Health Organization reports that 52 percent of people known to be infected with H5N1 have died from the disease.
The figure has been widely cited in academic papers, public health communications, and media reports, where it can provoke apocalyptic visions. “Bird flu pandemic could be ‘100 times worse’ than COVID,” claimed one New York Post headline. An article in The Guardian leads with the WHO’s “enormous concern” about the spread of H5N1, which, according to one lead scientist quoted, has an “‘extraordinarily high” human mortality rate.
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The actual picture, while still alarming, is more complicated. The WHO’s H5N1 mortality figure, an average of wildly different death rates from past outbreaks, doesn’t factor in mild cases that went undetected. Even less certain is how lethal H5N1 would be if it evolves to spread not just from animals to humans, but also from person to person.
The first step in combating any infectious disease outbreak is detection. Without widespread testing, health officials have little sense of who is infected, when to treat patients and how to monitor their close contacts.
In that sense, the bird flu outbreak plaguing the nation’s dairy farms is spreading virtually unobserved.
As of Monday, the virus had infected 157 herds in 13 states. But while officials have tested thousands of cows and are monitoring hundreds of farmworkers, only about 60 people have been tested for bird flu.
Officials do not have the authority to compel workers to get tested, and there is no way for workers to test themselves. In the current outbreak, just four dairy workers and five poultry workers have tested positive for H5N1, the bird flu virus, but experts believe that many more have been infected.
Five people who work at a poultry farm in northeastern Colorado have tested positive for the bird flu, the Colorado public health department reported July 14. (One of the cases awaits confirmation by the federal Centers for Disease Control and Prevention.) This brings the known number of U.S. cases this year to nine.
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The workers were likely infected by chickens, which they had been tasked with killing in response to a bird flu outbreak at the farm. The endeavor occurred amid a heat wave, as outside temperatures soared to 104 degrees Fahrenheit.
“The barns in which culling occurs were no doubt even hotter,” said CDC principal deputy director Nirav Shah at a July 16 press briefing. Wearing N95 respirators, goggles, and other protective gear was a challenge. Industrial fans whipped feathers around the facility that could have carried the virus, Shah added.
In this environment, the farmworkers collected hundreds of chickens by hand and placed them into carts where they could be killed by carbon dioxide gas within two minutes.
Dairy farmworkers often spend 10 to 12 hours a day milking dairy cattle in crowded, wet environments. They are in constant, intimate contact with unpasteurized cow milk, a known carrier of H5N1, the viral strain of bird flu that jumped from poultry to cows back in March.
But despite being the most exposed population to the virus, farmworkers are also offered few protections. To prevent the spread of bird flu among the general public, experts say we need to first protect the health of farmworkers.
“I don't want us to ignore what is happening right now, which is that farmworkers are getting infected with this virus,” said Jennifer Nuzzo, an epidemiologist at Brown University.
As bird flu spreads among dairy cattle in the U.S., veterinarians and researchers have taken note of Finland’s move to vaccinate farmworkers at risk of infection. They wonder why their government doesn’t do the same.
“Farmworkers, veterinarians, and producers are handling large volumes of milk that can contain high levels of bird flu virus,” said Kay Russo, a livestock and poultry veterinarian in Fort Collins, Colorado. “If a vaccine seems to provide some immunity, I think it should be offered to them.”
As bird flu spreads among dairy cattle in the U.S., veterinarians and researchers have taken note of Finland’s move to vaccinate farmworkers at risk of infection. They wonder why their government doesn’t do the same.
Excerpt: "We're flying blind," said Jennifer Nuzzo, director of the Pandemic Center at the Brown University School of Public Health. With so few tests run, she said, it's impossible to know how many farmworkers have been infected or how serious the disease is. A lack of testing means the country might not notice if the virus begins to spread between people — the gateway to another pandemic.
Excerpt: And while the federal government has made efforts to try to bolster the stockpile of supplies, “there hasn’t been a lot of transparency. It’s hard to gauge the sufficiency of it,” said Jennifer B. Nuzzo, director of the Pandemic Center at the Brown University School of Public Health.
Guest essay by Jennifer Nuzzo, excerpt: How worried you should be about H5N1, the bird flu virus spreading on dairy farms in the United States, depends on whom you are.
The Centers for Disease Control and Prevention has described the current H5N1 risk to the general public as low. The risk that the virus poses is tempered by the fact that it doesn’t spread easily among people — yet.
Right now public-health experts have the difficult task of urging authorities who can do something about H5N1 to take action, while maintaining public trust. Americans have just been through a pandemic that resulted in over one million U.S. lives lost. They may feel weary of more bad news or fear-based messaging. Communicating that while the threat level for most people is low, but if nothing is done it could become quite high, is not easy but is important.
Excerpt: “The concern about H5N1 has always been there,” said Dr. Jennifer Nuzzo, professor of epidemiology and director of the Pandemic Center at the Brown University School of Public Health. “But in the last couple of years, [the virus] started doing things that have been a bit unusual.”
“We’ve seen this virus start to infect mammals and a wide range of mammals,” she said, pointing at the different outbreaks throughout the world. “That’s a concern because humans are mammals, and so mammals are more like us than birds are.”
But what makes this recent outbreak the most concerning for Nuzzo is that the virus is now capable of infecting cows. “Cows are mammals that humans have a lot more contact with than all the other mammals that we’ve seen get infected,” she said.
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