A version of the H5N1 bird flu virus that killed a person in Louisiana and severely sickened a teenager in Canada has now been detected in dairy herds in Nevada.
The version, known as D1.1, is circulating in wild birds around the nation — causing massive die-offs in places such as Chicago, upstate New York and Ohio.
It’s different from the one known to be circulating in dairy cows and that has caused only relatively mild illness in humans (although it has killed scores of domestic and wild cats). Both versions belong to the H5N1 virus family— each with slightly different histories and genetic structures.
Finding D1.1 in dairy cows caught investigators off-guard, but it is also just the latest surprise as the H5N1 bird flu continues to flummox researchers and public health officials. It’s a stark reminder that this virus does not behave like a “typical” flu virus.
“I can’t overemphasize what a big deal it is,” said John Korslund, a former USDA scientist in an email. “This is truly a ‘s— show’ unfolding into a nightmare scenario. We have no idea how widespread this version of the virus already is in cattle herds. Every time poultry flocks break [with virus] we’ll need to investigate cattle contacts [which are many] as well as wild bird and other poultry contacts.”
Richard Webby, an influenza researcher in the department of infectious diseases at St. Jude Children’s Research Hospital in Memphis, Tenn., said while he thinks the findings are unlikely to change the risk outlook for the general population, it will affect the dairy industry.
Most researchers believed there was a singular contact event between a bird infected with H5N1 B3.13 and a dairy cow in the Texas panhandle, in late 2023. That one interaction led to an outbreak that has now affected more than 950 herds across 16 states and sickened 67 people — including 40 dairy workers.
But this new finding suggests such an occurrence was not a one-off — and that we may see more such spillover events from wild birds into cattle.
It is likely that H5 viruses (such as H5N1 or the H5N9 virus recently found in a commercial duck operation in Merced County) “will continue to be generated in wild birds and will continue to spill over to dairy cows,” he said. And some of these newer versions may have traits that allow them to spread more easily between cows — maybe via aerosols — or make the cows sicker. Not everyone agrees on the virus’ current mode of transport between cows, but most researchers point to milk.
Korslund said the discovery raises several questions that epidemiologists and health officials will need to address: How will it affect dairy workers? Dairy cows and feedlot cows? How about other livestock, such as swine, sheep, goats, and horses? What symptoms should farmers and veterinarians be on the lookout for? Will milk testing and reporting now require fields for both versions of the virus? Will herds who have been infected by B3.13 have immunity to D1.1?
And he’s worried about the political climate, and the appetite the Trump administration will have for this outbreak.
“So many unanswered questions yet on how this strain will behave in cattle,” he said. “We may have to hope that Canada does the research because our federal researchers appear to be temporarily paralyzed by the political process.”
Nevertheless, he urged health officials to begin testing livestock (not just dairy cows) in places with densely situated agricultural operations — such as in Ohio, where since Jan. 1, H5N1 (assumed to be D1.1) has been found in 40 commercial poultry farms in a two-county area.
“The entire livestock population in the area should be screened now to sort out susceptibility and viral hosting, given the circumstances,” he said.
But of all his worries, it’s the farmworkers at the viral battle front for whom he’s most concerned.
“No caring public health personnel can currently in good conscience recommend that sick, undocumented farm animal caretakers or flock depopulation employees get tested, knowing that ICE could show up at testing sites to demand citizenship verification,” he said. “Better to push the Tamiflu and recommend staying home a day or two… any worker testing initiatives are dead in the water and viral isolates will not be monitored for genomic changes by public health officials.”
