US detects H5N1 bird flu in a pig for the first time
Scientists are alarmed by the virus spreading to pigs, warning that this development brings it one species closer to a major human outbreak.
H5N1 bird flu has been detected in a pig on a backyard farm in Oregon, the USDA announced on Wednesday, October 30, 2024. This marks the first reported H5N1 case in a pig in the United States, with experts concerned about bird flu’s threat to humans.
The infection was discovered at a backyard farm in Crook County that keeps a mixture of animals, who share water and are housed together. The USDA says this setup has created the conditions for transmission of bird flu between species in other states.
H5N1 was first detected in chickens on the non-commercial farm on Friday 25 October. Just days later, one of the five pigs was also confirmed to be infected with bird flu. Despite not displaying symptoms, the pigs were all killed for further testing. The other animals on the farm, including goats, remain under surveillance.
"Animal pandemic"
This strain of bird flu has been spreading rapidly across the U.S. particularly among wild birds and poultry since 2020. In March of this year, H5N1 was detected in cows on dairy farms in Kansas and Texas, marking the first known instance of the virus in cattle. Just one month later, the CDC confirmed the first human case of H5N1, contracted after exposure to infected cows. Since then, the virus has spread to more than 400 cow herds across the U.S., with samples of pasteurized milk from grocery store shelves testing positive for remnants of the bird flu virus.
The number of humans testing positive for bird flu has now jumped to 36 known cases, with the infection rate accelerating rapidly; more than half of confirmed human cases were reported in the last two weeks.
At least 280 million birds and tens of thousands of mammals have died as a result of the H5N1 strain since October 2021. It has impacted animals in every continent except Oceania, from elephant seals in Antarctica to animals confined in zoos in Asia. The World Health Organization chief scientist Jeremy Farrar has called this an "animal pandemic."
Although the Centers for Disease Control and Prevention (CDC) state that the risk to the general public is currently 'low,' public health experts warn that each instance of the virus spreading increases the likelihood of it adapting to infect humans more easily.
Why scientists are alarmed by its spread to pigs
“It would take just one pig.”
So far, all humans infected with H5N1 have contracted the virus from another animal, with no evidence of human-to-human transmission. But with bird flu now being found in pigs, scientists are concerned that we are one step closer to that becoming a serious possibility. That’s because, unlike cows and birds, pigs can host both bird and human flu strains, acting as a 'mixing vessel' for viruses. This creates a dangerous opportunity for H5N1 to interact with a human virus, potentially gaining genetic mutations that could produce a new variant capable of spreading easily between humans.
"I would say the concern elevated slightly with this pig infection," Stacey Schultz-Cherry, a virus expert at St. Jude Children's Research Hospital and the deputy director of a World Health Organization center on animal and bird influenza, told Business Insider (BI).
Credit: The Conversation, CC BY-SA
“The detection of bird flu in a US pig is worrying,” Peter Stevenson, Chief Policy Advisor, Compassion in World Farming, said in a statement to Species Unite. “Pigs can be infected by avian, human and swine influenza viruses. Pigs can act as mixing vessels in which these viruses can swap genes and new viruses that are a mix of pig, bird and human viruses can emerge. This process appears to have been behind the 2009 swine flu pandemic. The U.S. Centres for Disease Control and Prevention has warned that if a pig was infected by a human and avian influenza virus at the same time a “resulting new virus might then be able to infect humans and spread easily from person to person”.
Similarly, the chief scientist of the UN health agency has said the risk of bird flu spreading to humans is an “enormous concern”. Over the past 20 years, in the hundreds of cases where humans have contracted the virus through animal contact, the mortality rate is above 50%.
“If it doesn’t spread from pigs to pigs and it just happened on that one farm, it’s not a big deal," Florian Krammer, a flu virologist at Mount Sinai’s Icahn School of Medicine in New York, told STAT. "If it starts to spread from pigs to pigs, then it’s much more of a problem,” he said. “If it ends up in large pig populations in the U.S. similar to cows, I think this would be a disaster.”
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