Bird flu among pigs should worry humans too

Spreading through big pig farms would give the virus ample opportunity to evolve into a form capable of causing a pandemic in humans. 

Pigs remain at the centre of scientists’ nightmare scenario because commercial swine carry lots of human flu viruses. Their cells share enough features with ours that flu viruses can use some of the same entry ports, known as receptors.

Fortunately, the case reported involved only a private backyard farm in Oregon. The infected pig was asymptomatic. A small potbellied pig on the same farm also tested positive. 

Also read: US Spots First H5N1 Bird Flu Case in a Pig, Raising Concern for Humans

All the pigs at the farm have been euthanized and the farm quarantined. So it’s not the start of a disaster, yet, but a warning that we must improve surveillance to better understand this virus.

Flu viruses have historically been transmitted from pigs to people and from people to pigs—either on farms or at agricultural fairs. The deadly 1918 flu jumped from people to pigs in the 1920s. 

It then jumped back into humans periodically, most recently in 2009, when it started a swine flu pandemic. That pandemic wasn’t as deadly as scientists initially feared, thanks to changes in the virus and our immunity.

People and pigs seem to exchange viruses through a respiratory route. Scientists back in 2014 found a flu called H3N2 was being transmitted back and forth between pigs and people, many of them kids, at Ohio state fairs. 

Adding to the threat is the fact that flu viruses are good at exchanging genetic material with each other. If a pig that already carried human flu got infected with the H5N1 bird flu, a new virus could emerge with parts of both, perhaps gaining the ability to infect us like the seasonal flu but with greater lethality.

Fears about H5N1 skyrocketed last spring, when the virus surprised farmers and researchers by turning up in dairy herds. Genetic analysis suggested the virus had been circulating undetected in cows since December 2023. A few dairy workers have become infected and recovered, while farm cats exposed to raw milk developed severe brain infections and died.

The Oregon pig infection looks like it came from infected chickens on the same small farm, which in turn were probably infected not by cows but by migrating wild birds, said Richard Webby, a specialist in influenza at St. Jude’s Children’s Research Hospital in Memphis. 

That doesn’t detract from the concern. “We need to understand what’s going on in cows. But, you know, there is also this virus flying north and south above our heads," he said.

Also read: Bird flu outbreak ’100 times worse’ than Covid pandemic, say experts

The H5N1 bird flu first became a concern in the late 1990s. Early cases showed the virus was about 50% lethal in humans. Outbreaks waxed and waned, though in 2022 something strange started happening— vastly more birds and mammals all over the world were getting infected and, in many cases, dying. There were outbreaks among foxes, bears, raccoons, sea lions, porpoises and minks.

Though this jump to pigs on one small farm was contained, Webby said it would be good to see an uptick in surveillance in swine, other animals, and in humans. 

Even if local doctors or vets don’t have specific tests for H5N1, red flags might be triggered if people test positive for this same class of flu—influenza A—but test negative for the known subtypes of seasonal flu.

Meanwhile, the outbreak in cows still festers. So far, they’ve seen no new variants that would pose an increased risk to humans, said Webby. “But that’s the problem with flu … just because we haven’t seen it yet doesn’t mean it’s not going to happen tomorrow."

The earlier scientists can detect a potentially dangerous outbreak in pigs or people, the better the odds it can be contained. Scientists also need to conduct more research to understand this virus—especially the version spreading in cows, which, in other animals, is one of the nastiest they’ve seen. It causes massive brain infections in cats, ferrets and some other mammals, although most human infections have been mild.

Why? “I think a lot of people are trying to figure that out," Webby said. It might be related to different animals’ biology or to how they’re exposed. It may be far worse for animals eating infected prey or, in the case of cats, drinking lots of infected raw milk. 

Also read: Bird flu: Surging outbreaks raise human-infection risk. Here’s what 3 UN agencies said

While bird flu won’t necessarily cause a pandemic, the trend is ominous, as if it’s testing the waters in ever more species. Every time it succeeds, it increases its chance of drawing a winning lottery ticket of genes. If it wins, we lose. ©bloomberg