Here’s a startling fact: the mammary glands of both domesticated livestock and humans could be harboring avian influenza, and this discovery has far-reaching implications for public health and agriculture. But here’s where it gets controversial: while we’ve long focused on poultry as the primary source of avian flu, recent findings suggest that other animals—and even humans—might play a bigger role in its spread than we ever imagined. And this is the part most people miss: it’s not just about birds anymore.
Since 2022, a highly pathogenic avian influenza outbreak has devastated over 184 million domestic poultry. But the real shock came in spring 2024 when the virus made an unprecedented leap to dairy cattle, infecting more than 1,000 milking cow herds. Now, a groundbreaking study led by Iowa State University researchers reveals that the mammary glands of pigs, sheep, goats, beef cattle, and even alpacas are biologically primed to harbor the virus, thanks to high levels of sialic acids—a sugar molecule that acts as a gateway for influenza viruses to infect cells.
Rahul Nelli, the study’s lead author and a research assistant professor, puts it bluntly: ‘The main thing we wanted to understand is whether there is potential for transmission among these other domestic mammals and humans, and it looks like there is.’ This raises a critical question: Could these animals become silent carriers, spreading the virus to humans or other species without showing obvious symptoms?
Sialic acid, found on the surface of many animal cells, acts like a microscopic docking station for influenza viruses. Last year, the same research team discovered high levels of sialic acid in dairy cattle udders, which explained why the H5N1 avian flu spread so rapidly among dairy herds. But the plot thickens: their latest study, published in the Journal of Dairy Science, found these same receptors in human mammary glands. Is this the missing link in understanding how avian flu could jump to humans more easily?
While only a few sporadic cases of H5N1 have been reported in the animals studied, Dr. Todd Bell, a co-author, warns, ‘If we don’t look, we don’t know.’ This lack of widespread testing leaves a gaping hole in our understanding of the virus’s reach.
The implications are alarming. In dairy herds, H5N1-infected cows are producing milk contaminated with the virus, prompting the USDA to launch nationwide surveillance of raw milk samples. While pasteurization kills influenza viruses, making store-bought milk safe, raw milk from other mammalian livestock poses a risk. Should we be rethinking our consumption habits altogether?
Nelli highlights another concern: ‘Some people do consume the raw milk of these other animals.’ The presence of the virus in milk from infected cows likely fuels its spread, increasing the risk of transmission to humans. ‘If a virus in livestock is being spread by respiratory infections, few humans will be in close enough contact to catch it. But milk is an entirely different situation because it’s transported into communities,’ he explains.
What’s even more unsettling is that the mammary gland tissues examined in the study contain sialic acid receptors favored by both avian influenza and seasonal human flu. This raises the specter of these viruses mingling and mutating into something far more dangerous. Historically, H5N1 has had a 50% fatality rate in humans, though the current outbreak has resulted in only two deaths out of 71 confirmed cases. But what if the virus evolves into a more transmissible or deadly strain?
Bell urges, ‘We need to try to stay ahead of this so it doesn’t have a chance to continue to replicate and potentially evolve into something even more troublesome.’ The question now is: Are we doing enough to monitor and mitigate this risk?
What do you think? Should we be more cautious about raw milk consumption? Or is the risk overblown? Let’s discuss in the comments—this is a conversation we can’t afford to ignore.
