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US Faces Growing Threat of H5N1 Avian Influenza in Dairy Cows

The virus has spread to 17 states and infected nearly 1,000 dairy herds, raising concerns about human transmission and economic impact.

PETALUMA, CALIFORNIA - FEBRUARY 18: Eggs move on a conveyor belt through an egg washer at Sunrise Farms on February 18, 2025 in Petaluma, California. As egg prices continue to skyrocket due to the avian flu outbreak, egg farmers are having to invest millions of dollars in biosecurity efforts to keep their flocks safe. Fourth-generation egg farm Sunrise Farms in Petaluma, California lost 550,000 chickens to avian flu in December of 2023, marking the first time in 112 years that the main family farm had no chickens. It took Sunrise Farms over a year to rebuild their flock to 900,000 chickens that produce nearly 500,000 eggs a week. (Photo by Justin Sullivan/Getty Images)
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Overview

  • H5N1 avian influenza was first identified in US dairy cattle in March 2024, with three confirmed crossover events from birds in Texas, Colorado, and Arizona.
  • The virus has now affected dairy herds in 17 states, with over 970 herds testing positive, and has been linked to 70 human cases, primarily among those with exposure to infected dairy cattle or poultry.
  • Milk from infected cows is a key vector for virus transmission, though pasteurization effectively eliminates the threat; raw milk consumption poses higher risks.
  • The USDA has launched a national milk testing program and approved field trials for a dairy cow vaccine, but recent funding prioritizes poultry, leaving dairy cattle biosecurity gaps.
  • Experts warn that the virus's persistence in dairy cattle and poultry increases the risk of human transmission and potential evolution into a pandemic strain.