Spillover UK on alert after H5N1 bird flu spills over to sheep in world-first The UK sheep had inflamed mammary gland much like infected cows in US. Beth Mole Mar 24, 2025 6:32 pm | 0 Sheep in Yorkshire Dales. Credit: Getty | Edwin Remsberg Sheep in Yorkshire Dales. Credit: Getty | Edwin Remsberg Story textSizeSmallStandardLargeWidth *StandardWideLinksStandardOrange* Subscribers only Learn moreThe H5N1 bird flu has spilled over to a sheep for the first time, infecting a domesticated ruminant in the United Kingdom much like it has in US dairy cows, according to UK officials.The single sheepa ewein Yorkshire, England, was confirmed infected after captive birds on the same property had tested positive for the virus, according to an announcement Monday. The ewe's milk was found to be positive for the virus through a PCR test, which detected genetic signatures of the virus. The ewe also had H5 antibodies in its blood. At the time of the confirmation, the ewe had symptoms of the infection in the way of mastitis, inflammation of the mammary glands.This mirrors what US dairy farmers have been seeing in cows. An outbreak of H5N1 in dairy cows erupted a year ago, on March 25, 2024. Since then, at least 989 herds across 17 states have been infected with bird flu. In previous reports, farmers and researchers have noted that the virus appears to attack the animal's mammary glands and their milk is teeming with the virus.In the US, at least 70 people have been infected with the virus, 41 of whom were dairy workers. In some cases, workers reported having milk splashed on their faces before developing an infection. While nearly all of the cases have been relatively mild so farsome only with eye inflammation (conjunctivitis)one person in the US has died from the infection after being exposed via wild birds.In the UK, officials said further testing of the rest of the sheep's flock has found no other infections. The one infected ewe has been humanely culled to mitigate further risk and to "enable extensive testing.""Strict biosecurity measures have been implemented to prevent the further spread of disease," UK Chief Veterinary Officer Christine Middlemiss said in a statement. "While the risk to livestock remains low, I urge all animal owners to ensure scrupulous cleanliness is in place and to report any signs of infection to the Animal Plant Health Agency immediately."While UK officials believe that the spillover has been contained and there's no onward transmission among sheep, the latest spillover to a new mammalian species is a reminder of the virus's looming threat."Globally, we continue to see that mammals can be infected with avian influenza A(H5N1)," Meera Chand, Emerging Infection Lead at the UK Health Security Agency (UKHSA), said in a statement. In the US, the Department of Agriculture has documented hundreds of infections in wild and captive mammals, from cats to bears, raccoons, and harbor seals.Chand noted that, so far, the spillovers into animals have not easily transmitted to humans. For instance, in the US, despite extensive spread through the dairy industry, no human-to-human transmission has yet been documented. But, experts fear that with more spillovers and exposure to humans, the virus will gain more opportunities to adapt to be more infectious in humans.Chand says that UKHSA and other agencies are monitoring the situation closely in the event the situation takes a turn. "UKHSA has established preparations in place for detections of human cases of avian flu and will respond rapidly with NHS and other partners if needed."Beth MoleSenior Health ReporterBeth MoleSenior Health Reporter Beth is Ars Technicas Senior Health Reporter. Beth has a Ph.D. in microbiology from the University of North Carolina at Chapel Hill and attended the Science Communication program at the University of California, Santa Cruz. She specializes in covering infectious diseases, public health, and microbes. 0 Comments