The ongoing bird flu outbreak in the US is now the longest and deadliest on record. More than 57 million birds have been killed by the virus or culled since a year ago, and the deadly disruption has helped propel skyrocketing egg prices and a spike in egg smuggling.

Since highly pathogenic avian influenza (HPAI) A(H5N1) was first detected in US birds in January 2022, the price of a carton of a dozen eggs has shot up from an average of about $1.79 in December 2021 to $4.25 in December 2022, a 137 percent increase, according to data from the US Bureau of Labor Statistics. Although inflation and supply chain issues partly explain the rise, eggs saw the largest percentage increase of any specific food, according to the consumer price index.

And the steep pricing is leading some at the US-Mexico border to try to smuggle in illegal cartons, which is prohibited. A US Customs and Border Protection spokesperson told NPR this week that people in El Paso, Texas, are buying eggs in Juárez, Mexico, because they are "significantly less expensive." Meanwhile, a customs official in San Diego tweeted a reminder amid a rise in egg interceptions that failure to declare such agriculture items at a port of entry can result in penalties up to $10,000.

Foul effects

Still, America's pain in grocery store dairy aisles likely pales compared to some of the devastation on poultry farms. HPAI A(H5N1) has been detected in wild birds in all 50 states, and 47 have reported outbreaks on poultry farms. So far, there have been 731 outbreaks across 371 counties. At the end of last month, two outbreaks in Weakley County, Tennessee, affected 62,600 chickens.

With the outbreak at the one-year mark, it is the longest bird flu outbreak on US record. And with 57 million birds dead across 47 states, it's also the deadliest, surpassing the previous record set in 2015 of 50.5 million birds in 21 states.

Although the virus is highly contagious to birds—and often fatal—the risk to humans is low. The Centers for Disease Control and Prevention notes that the avian influenza Type A viruses (aka bird flu viruses) generally don't infect humans, though they occasionally can when people have close or lengthy unprotected contact with infected birds. Once in a human, it's even rarer for the virus to jump from human to human.

In the current outbreak, the CDC has tracked more than 5,000 people who have had contact with infected birds but only found a single case of bird flu in a human. The reported case in Colorado came from a person who worked directly with infected birds and was involved with a cull. The person had mild symptoms and recovered.

Flu fears

Although the current data is comforting, virologists and epidemiologists still fear the potential for flu viruses, such as bird flu, to mutate and recombine into a human-infecting virus with pandemic potential. A report published in the journal Eurosurveillance on January 19 highlighted the concern. Researchers in Spain documented an outbreak of avian flu among farmed mink on the northwestern coast during October of last year. The mink were likely infected via wild seabirds, which had a coinciding wave of infection with H5N1 viruses at the time. Over the course of October, more and more mink fell ill, suggesting mink-to-mink transmission, which led to the culling of the entire colony of nearly 52,000 animals starting in late October.

Notably, the H5N1 virus infecting the mink had an uncommon mutation that may have enabled it to spread to and among the mink. Mammal-to-mammal transmission of an avian virus alone is noteworthy, but it's particularly concerning in mink, which can act as viral blenders. As the authors of the Spanish report note:

Experimental and field evidence have demonstrated that minks are susceptible and permissive to both avian and human influenza A viruses, leading to the theory that this species could serve as a potential mixing vessel for the interspecies transmission among birds, mammals and human.

As such, the authors say it is necessary to "strengthen the culture of biosafety and biosecurity in this farming system and promote the implementation of ad hoc surveillance programs for influenza A viruses and other zoonotic pathogens at a global level."

None of the workers on the mink farm became infected with the H5N1 virus, the authors report. However, they note that using face masks was compulsory for all mink farm workers in Spain following concerns over the spread of SARS-CoV-2. And upon the first detection of an illness at the farm, the workers there took precautions in case it was SARS-CoV-2, which included using disposable overalls, face shields, face mask changing twice per day, and frequent hand washing, all beginning on October 4.