Should We Be Worried About Bird Flu?

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In December, 2021, a few weeks after the Omicron variant emerged to spark a new, punishing phase of the COVID-19 pandemic, Jim Lester's birds got sick. Lester, who owns an exhibition farm in Newfoundland, Canada, learned that the culprit wasn't the novel coronavirus but the first known outbreak in North America of a highly pathogenic strain of bird flu, called H5N1. Hundreds of birds were infected and died. Scores more—peacocks, geese, an emu—had to be culled. They all "had personalities," Lester said. "It was a true tragedy." Since then, the virus has propagated down through the Americas, killing tens of millions of birds and, perhaps more concerning, infecting dozens of mammalian species: bottlenose dolphins in Florida; sea lions in Peru; elephant seals on the islands near Antarctica. Now, for the first time, the virus is circulating among cattle, and at least thirty-four herds across nine states in this country are known to be infected. Last month, the Food and Drug Administration announced that one in every five samples of milk in the United States carries fragments of the virus, suggesting an even wider spread. One expert called the situation "totally unprecedented."

Influenza is a promiscuous pathogen. Its potential to unleash pandemics is due partly to the modular structure of its genome, which allows it to swap segments of its genetic material wholesale when different versions of the virus co-infect a cell. This occurred in the mid-nineties, when H5N1 was first isolated, from a goose in southern China, and went on to infect some twenty per cent of the poultry in Hong Kong markets, precipitating the slaughter of more than a million and a half chickens. In the intervening decades, the virus has periodically caused devastating outbreaks in poultry, but it remains poorly suited to the human respiratory tract, and that has limited its spread among people. Still, for those who do get infected—usually farmworkers and others with exposure to animals—the effects can be lethal. In some prior outbreaks, the virus inflicted a case-fatality rate of more than fifty per cent. Fortunately, only two people in the U.S. are known to have been infected, and both experienced mild symptoms. Since 2022, only about two dozen human cases have been recorded worldwide, and, according to the Centers for Disease Control and Prevention, the risk to public health remains low.

The prevalence of the virus in our milk supply may also be less alarming than it sounds. The P.C.R. test used to identify it can detect minuscule amounts of genetic debris, and a positive result does not imply that the virus is alive, much less contagious. Nearly all milk sold in the U.S. is pasteurized—heated to destroy potential pathogens—and that process may be especially effective for unstable viruses such as influenza. (Many states—some, recently, as part of a broader backlash against public-health measures—have legalized the sale of raw milk, which health officials generally do not advise consuming.) The tests needed to conclusively determine whether pasteurization kills H5N1 take time and involve injecting eggs with milk samples, but, according to the F.D.A., preliminary studies haven't found any traces of live virus.

It now seems likely that H5N1 was first transmitted from a bird to a cow late last year, and that the virus has been circulating unchecked among cattle for months. Many cows who shed the virus don't show symptoms, and how it spreads among them remains a mystery. Contamination of milking equipment is the most probable route, but respiratory transmission is also a possibility. So far, pigs haven't contracted the virus, which is good for them—and us. Pigs have receptors for both avian and human versions of the flu, so they can serve as "mixing vessels," facilitating genetic exchange in ways that could spawn a mutant capable of spreading among people and igniting another pandemic.

In the unlikely event of that emergency, we're far better positioned than we were for COVID. Influenza may be the world's most familiar viral pathogen—its genome, virulence, and transmission patterns have been studied for decades. The U.S. has a large stockpile of Tamiflu, which should work against bird flu, as it does for other influenza strains, and which could be given to an infected person's contacts to mitigate spread. Health officials have also indicated that they could rapidly scale up testing and, if needed, shift the nation's annual flu-vaccine production to shots that are tailored for H5N1.

But the ability to respond is not the same as responding. The country's initial approach has had an unsettling resonance with the first months of COVID. Because there is no widespread program to screen farm animals for H5N1, we have little sense of how many have been tested or what proportion of tests have been positive. It took a month after bird flu was detected in cattle for the Department of Agriculture to require that lactating cows be tested before crossing state lines, and the agency has since clarified that only thirty animals in a group must be tested, irrespective of how large the group is. Last month, when the government released genetic sequences for scientists to study, it did not share information about where or when the samples were collected, making it difficult to track how the virus is spreading and evolving. Meanwhile, we haven't conducted antibody studies of farmworkers that could determine the extent to which they are getting infected; we'll know they're sick if they show up in emergency rooms.

Many hospitals, of course, are still reeling from the pandemic, and leaders have expressed concern that they don't have the staffing, the resources, or the morale to contend with another crisis. The deeper problem, though, is the country's COVID hangover. America has emerged from the pandemic not just fatigued, but resentful and divided. If bird flu becomes human flu, one gets the sense that our principal fight won't be with the virus, but with one another.

In Albert Camus's novel "The Plague," the vectors of disease are not birds but rats. The authorities are slow to act and, as the death toll mounts, people grow depressed, distrustful, violent. Even when the crisis eventually recedes, a doctor comes to feel that plague "never dies or disappears for good." He notes, "Perhaps the day would come when, for the bane and the enlightening of men, it would rouse up its rats again and send them forth to die in a happy city." The rise of pandemic pathogens is an inextricable part of the modern world. The scale of their destruction doesn't have to be. ♦