In spring, consumers in the United States found themselves having to hunt for something that had previously been exceedingly easy to find: eggs. Some supermarkets limited customers to a single carton per visit, but still ran out. Shoppers who did manage to find eggs in stock paid dearly — a dozen could sell for more than US$11. For many people, it was the first indication that the country was in the midst of a devastating bird-flu outbreak.
The H5N1 flu virus responsible for this outbreak hit poultry farms especially hard. The egg shortage and skyrocketing prices were the result of the loss of tens of millions of hens — the US Department of Agriculture (USDA) requires the destruction of poultry flocks that test positive for H5N1. Egg prices have now fallen. But US consumers could experience another shock if they buy a turkey for their Thanksgiving meal in late November. This year’s flock is the smallest in decades, partly due to bird flu. Some economists predict that turkey prices will be 40% higher this year than in 2024.
Nature Spotlight: Influenza
Some poultry farms contracted H5N1 from waterfowl. But others got the virus from a new source of infection. In March 2024, the United States announced that several herds of dairy cattle had been infected. Since H5N1 jumped to cattle, the virus has infected at least 1,000 cows in 18 states, tens of millions of chickens and turkeys, and 70 people, one of whom died.
H5N1’s move into dairy cattle, which come into close contact with humans, has infectious-disease specialists on alert. “This was not on our potential-pandemic bingo card,” says Thomas Friedrich, a virologist at the University of Wisconsin–Madison. The virus hasn’t developed the capacity to easily transmit between humans, but that doesn’t mean that it never will, he adds. And “we’re not doing enough to take the threat as seriously as I think we should”.
In April 2024, the federal government began requiring dairy farmers to test cattle for H5N1 before moving them between states. And late last year, it launched a milk-testing programme. But it’s not enough, says Carol Cardona, an avian-influenza researcher at the University of Minnesota in Minneapolis. “We want to see a comprehensive national plan that addresses all susceptible species,” she says. Dairy cows are among the latest species to contract H5N1, but they won’t be the last.
The current clade of H5N1 circulating the globe has been detected in dozens of animal species, including cats, seals and mice. Specialists worry that the more the virus circulates in mammals, the greater the chance it will acquire the mutations it needs to transmit between humans, sparking a global pandemic. “If we don’t take and maintain steps to actively detect infection of cattle and then, when it’s detected, to stop the spread of virus from farm to farm, then the danger persists,” Friedrich says.
First contact
When Kay Russo, a veterinarian at RSM Consulting in Fort Collins, Colorado, heard about a mystery illness circulating in dairy cattle in Texas, she worried that it might be avian influenza.
The United States has introduced a milk-testing programme to monitor the H5N1 virus.Credit: Michael M. Santiago/Getty
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