The detection of highly pathogenic avian influenza (HPAI) in dairy cows that had a puzzling illness syndrome, announced earlier this week, was a stunning twist in the story of a H5N1 virus that has been circulating globally, including in US birds since early 2022.
As federal veterinary officials and their state and local research partners continue their investigations, the findings have prompted a flurry of new questions among livestock and influenza experts. For now, they say it's not clear if HPAI was the only cause of the mystery illness in cows. Also, experts say the presence of dead wild birds that carried the virus at affected farms raises new issues about biosecurity in livestock settings.
In a notification yesterday to the World Organization for Animal Health, the US Department of Agriculture (USDA) said H5N1 is the subtype and belongs to the 2.3.4.4b clade, which has been circulating in many world regions and has spread all the way to Antarctica. The virus isolated from the cow samples descended from the B3.2 genotype first seen in wild birds in November 2023. An analysis found no markers for mammalian adaptation or antivirus resistance.
Is HPAI the sole cause of symptoms?
Joe Armstrong, DVM, a cattle production expert with the University of Minnesota, in a special episode of the University of Minnesota Extension's Moos Room podcast about beef and dairy issues, said the unexplained illness syndrome had been reported in certain dairy herds in the Texas panhandle and other locations since late January and early February.
Over several weeks, the animals were tested extensively for different illnesses, he said. "When they started coming up short on everything, they started thinking outside the box about what this could possibly be, and they started testing for highly pathogenic avian influenza."
So far, there's not enough evidence to confirm that HPAI is the sole cause of the symptoms, Armstrong said. More testing is needed in cows that fit the case profile. About 10% of the herds on outbreak farms were affected, especially mature mid-to-late–lactation cows, resulting in a 10% to 20% reduction in milk production.
Armstrong said the illness profile is unusual because veterinarians are more likely to see illnesses in young stock.
He said the illness in cows lasts 10 to 14 days, peaking at about day 5 with a sudden drop in milk that is thicker and yellowish, similar to colostrum. Some of the animals had secondary illnesses, including mastitis and pneumonia.
The good news is that sick cattle are not dying, but the lack of necropsy tissues makes for a tricky diagnostic situation, Armstrong said. "So we're not getting a chance to look at as many samples and full sets of tissues as we normally would."
New biosecurity threats?
Jeff Bender, DVM, who directs the Upper Midwest Agricultural Safety and Health Center at the University of Minnesota and is a professor and hospital epidemiologist at the university's School of Public Health, told CIDRAP News that infected wild birds—already identified as the source of the virus—raise big questions about biosecurity on farms going forward.
"Feed security is one answer, but are there other ways to discourage wild bird contact?," he asked. Experts have said shared contaminated water sources are another likely source and are thought to have played a role in the recent spread of the virus from poultry to baby goats at a farm in western Minnesota.
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Categories: Minnesota, Livestock, Dairy Cattle